Hacking Downgrading CFW 3DS Firmware

[KleinesSinchen]

I wouldn't start messing around if you do not have the means to recover from a brick.
This mean soldering wires to your 3ds and using a SD card reader to write back a backup NAND.

There is no reason to do that on a 3DS anymore. Anything (and more) what hardmod can do, can also be done with ntrboot.

And then there's me and my N3DS, which I haven't touched since the Switch came out and it's still on v11.7U firmware, the last one without the sneaky telemetry that v11.8U introduced.

Telemetry? https://www.3dbrew.org/wiki/11.8.0-41
Not updating is/was rather not and option for people using eShop and/or online gaming.
I've no idea if there are actually games not working on 11.7, but generally not updating a 3DS makes no sense once B9S is installed.
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Downgrading experiments are mostly useless and can lead to the console not booting
But as long as B9S is still present – which should be the case thanks to Luma3DS FIRM0/FIRM1 protection – restoring a previously created backup is a trivial thing.
Both, the downgrade, and potentially repairing with NAND restore takes only minutes. Generally very unsafe are downgrades below the version minimal required by the device. That would be

• 6.0 for O2DS
• 9.0 for N3DS(XL)
• 11.5 for N2DSXL

 

[SylverReZ]

Ntrboot is highly recommended if you want to mod your 3DS. I suggest using an Ace3DS X since it already has ntrboot preflashed onto the card, so you don't need to use the flasher app to program it.

https://3ds.guide/ntrboot
https://flashcarts.net/ds-quick-start-guide