The big differences in architecture are arm, x86-64(soon to be split into v1 and v2+ if it hasn’t been already), i686 which is almost all 32 bit intel and i386(no one is actually using this!)
Not to join the chorus of model train enthusiasts itt, but Debian still maintains i686. Gentoo from source is another great option. There’s arch32 as well which I think requires that you be at least a p3.
Arm is still in a weird place and it depends on the particular implementation more often than not:
There’s Debian for arm sbcs, and there’s a different, less normal armbian that is more cheap/weird sbc oriented but also sucks in various ways. Theres also arch and gentoo for arm as well.
M1 Mac users will probably want asahi.
Actual factual i386 needers (pre-pentium) will want to run either the gentoo or bsds maintained specifically for that purpose.