Working on softmodding a 3DS running 2.1.0-4E and https://github.com/hax0kartik/pre9otherapp/releases says to "Use usr2arm9ldr to support pre 4.0 firmwares."
Unfortunately, I can't find usr2arm9ldr and 3ds.hacks.guide says to get the the latest release of pre9otherapp (the .bin file corresponding to your firmware version), which points to the latest version which doesn't delineate between firmware versions.
I was going to use an older .bin, but https://gbatemp.net/threads/am-i-bricked.480331/page-2 seems to have bricked their 3ds by using the wrong .bin
Unfortunately, I can't find usr2arm9ldr and 3ds.hacks.guide says to get the the latest release of pre9otherapp (the .bin file corresponding to your firmware version), which points to the latest version which doesn't delineate between firmware versions.
I was going to use an older .bin, but https://gbatemp.net/threads/am-i-bricked.480331/page-2 seems to have bricked their 3ds by using the wrong .bin