Old 3DS can't run Homebrew launcher, following 3ds.hacks.guide : r/3dspiracy
Homebrew Launcher (Soundhax)
Nintendo 3DS Releases: Luma3DS 10.0 with Network Time Client, Blue Light Filters and more; 3DS Homebrew Menu 2.1.0 and TWiLightMenu++ 8.5.0 released and 3DS Shell updated to version 4.3.1 - Wololo.net
3DS Hacks - Installing Games and Homebrew Apps - CFWaifu