I only recommend updating firmware if there is a game or update that needs a higher firmware. Otherwise, you do not need to update your firmware at the moment.
It is as thorough as one can get from the general community. The only way to really narrow it down is to get a list of all homebrew apps a user has used but that list can get really long and even veteran users can struggle to remember everything they've installed so its not a fair question. Also, while majority of reports are old, there are still reports that have come in within the last year so its as much relevant as any other source of information.
I also really need to reiterate this point because you, as well as many others, are guilty of this belief. ReSwitched is not gospel. There have been multiple times when they have been wrong such as with the capabilities of the TX team so there is legitimate reason to doubt even their knowledge base. Not to mention that they are not the ones who determine who gets banned but Nintendo but unless one of them secretly works for Nintendo, we will never found out the criteria for bans. Therefore as a community, we are forced to rely on learning information about bans secondhand because telemetry only matters if it results in a measurable outcome which is a ban. The same thought process was used during the 3DS era so dismissing the community seems like a step backward especially when, as I said, these reports are in the hundreds. You might be able to argue that one or two users may have misreported information but with this large of a sample size, either you have to acknowledge there might be truth in the reports or its a large group effort to misrepresent ban data which is borderline conspiracy.
You also have to understand that I am not saying you use Atmosphere, you will get banned. I always say there is a chance because that is the objective truth. What that chance is was never my intention nor something I planned on discovering. Its like the chances of being struck by lightning, attacked by a shark, or contracting COVID. Some people think those chances are negligible or downright nonexistent while others will take precautions for fear of becoming the next statistic. The point is the chance still exists and should not be dismissed because it has not personally happened to you. Look at the exFAT issues. Many people dismissed it because it had not happened to them yet but once it did, they became a believer. You are doing the same thing as those people. While your friends and family may have been lucky in not getting banned, I have observed the opposite but also my fair share of people who have avoided the ban hammer despite doing supposedly "ban-worthy actions". So who is more likely to be right, the stance that dismisses hundreds of people within the community or the one that acknowledges multiple outcomes?
Its true that we don't know the specifics about what nintendo actually bans for, but you previously said they ban at random, which is very unlikely. Its more likely that we are missing some info, either on the what gets people flagged for a ban, or on the ban report.
If just CFW would ban people, it would be likely that at least one of my friends, families or my own switches would be banned by now, after many years running only CFW or a mix of CFW and full stock.
Also the atmosphere devs aren't perfect, true, they also make mistakes, but they know more about what the switch stores, what modules have access to and what the switch sends to Nintendo, then most other people, so they more likely know what can even lead to a ban in the first place, and what the switch can't detect/doesn't send.
They also weren't completely wrong about SXOS, since TX never made a full CFW themself, and instead was proven to use atmosphere source code for sxos.
Its also not as if they ignored every ban they heard about, they got more info from those people, and normally it was possible to map the reason for the ban to some of the known sources of bans.
About the amount of data, bad data even in big amount might not be helpful to determine a general answer like can CFW lead to bans, but it can help identify tendencies, like Game NSPs are more likely to ban. But bad data can but can also misslead and waste time during analysis.
Generally this is info I'm pretty confident about:
Game NSPs/XCIs
* Going online while using an installed backup leads to a quick ban
* Using an XCI via card emulation offline seems to be mostly save, but could potentially lead to a ban later on
* Using an NSP offline doesn't always lead to ban directly, but has the potential to lead to a ban over time, when some info about tickets is send to nintendo
Homebrew NSPs/Prebuild Romhacks with their own titleId
* This leaves a lot of obvious traces, and will probably lead to a ban even without actively using it
Home Menu icon replacements
* Its unclear weather this is safe, so better don't do this on an offline nand
Changing the user icon via homebrew/dev menu
* This has already lead to bans in the past and should not be done when going online
Abnormall/sketchy eshop/cdn requests
* This has also already banned many people, especially if you are trying to acces things you should not be able to access
* Its also somthing that can ban relativelly quick
Backup restore/log clearing
* This is one of the points that could or could not ban people, but its something nintendo can identify, so its better to not touch it unless something worse like a brick or a guranteed ban could be prevented by it
Sketchy Log (e.g. devmenu logs on a retail game, or logs for the wrong games)
* This has also lead to bans in the past, so better not do this on a nand that goes online, through it might be possible that atmosphere prevents enough telemetry from happening by now, so that this is not necesarrily a problem anymore while used offline
Save Game editing
* This is heavilly dependend on the game. A game like splatoon syncronises a lot with the server, so it can identify a lot of modifications, other games might not result in any ban, even if you use a fully modified and completed save game thats wasn't modified perfectly.
Rom hacks via layered fs
* This is another things thats heavilly game and mod dependend, but generally is more liekyl. Some games can be modded even online, some games allow some mods online, other will ban you when using mods online or even when you go offline without the mod, but with a savegame used in the mod
Cheating
* This is also game dependend, some games have no real cheat detection and will allow you to cheat online until reaported, or cheat in private lobbies, other could be mostly single player games with some online component, that could ban you even when you are just cheating in the single player, so better cheat offline unless you know the specifics for the game or want to risk a ban over time
Error logs from homebrew
* This had lead to problems in the past, but by now is handled by atmosphere by blocking them getting added to the telemetry send to nintendo
Prodinfo blanking
* Likely safe, but might lead to some weird logs that might be idenfiable when going online on a nand that had it active
Downgrading via Daybreak
* Nintendo might be able to idenfify this so its likely good not to do this unless there is no other way, but it might also be safe
Emummc
* Emummc itself is safe, but it adds potential sources of error and mixing nands that connect to nintendo can lead to a ban
Resized/bigger nands
* This could be detected by nintendo in theory, but seems to be used online by some people without a ban. But staying in CFW all the time might be better here to reduce the amount of telemetry send to nintendo
Signature patches
* Signature patches by itself seem to be fine as far as I know, but they add potentiall to screw up by starting the wrong homebrew while not paying attention
* I'm also unsure if they might also negativelly affect data corruption detection to a degree, that might result in other problems that could lead to a ban
What didn't get verified as a ban cause yet, so it likely safe:
* Atmsophere with its defaults online/offline
* Most normal homebrew (Emulators, game ports...) when run via Applet or by holding R when starting a game
* Custom Themes, through they need to be delete on every update of qlaunch
* Most Custom Sysmodule (like SysDVR, Sysclk)
* Updating via daybreak (Its like updating from a gamecard when offline)
* Things that happen outside of HOS and don't affect it like Linux and android
There might be more potentiall exotic ban triggers that we don't know yet that someone might trigger and get banned. There is also always user error, so the chance for a ban is never really 0% the moment you touch custom firmware.
So I don't think addind more complexity and potential points of error for people that just want to run some homebrew really helps the user or the data about whats getting people banned, so I normally recommend those people my setup, with just Atmosphere and hekate+whatever homebrew you want to use. This runs mostly safe with less potential to screw up.
