Yeah as far as I am aware most hardmods for the 3ds family don't have much merit these days over software options. Flash carts might have some merit as well (stuff like the sky3ds being drag and drop, and able to be dropped into whatever 3ds you like) but they are not going to be able to play things softmods can't, and if you are contemplating soldering something then even less merit.
Hardmods are then mostly relegated to video out mods (hard to find nowadays. There are some limited options for software capture but hardmods suffer fewer pitfalls), automated/turbo button press, loudness mods for headphones (they have a resistor to limit max volume to comply with various country laws and not blow out the eardrums of kids with earbuds, which is a serious problem -- https://www.healthline.com/health-news/are-your-kids-headphones-permanently-damaging-their-hearing#2
) and maybe a brightness mod or two. NAND backup and restore stuff was a thing but today we have total control so just edit your save instead, and yeah some of the softmod stuff stands a better chance of bringing things back from the brink without having to worry if you have a vaguely current backup. Likewise some did transplant things before we got softmods able to mimic whatever region you wanted.
Basically if your desires are to play whatever games the 3ds has to offer (not many from where I sit but that is a different discussion), use some cheats
, maybe load a few ROM hacks, use the odd bit of homebrew or hacked emulator, and still stand a reasonable chance of restoring things if you do something silly with the menu or something then softmods are where it is at. A flash cart (especially a good DS one) might make some aspects easier, or give you some more storage, so maybe flank it with one but even then you are not gaining much in an overall sense.