I'm not sure if Discord has options to fall back to H.263 like the open standards world (SIP) does, but that's the classic codec from 1995 and would definitely

I'm not sure if Discord has options to fall back to H.263 like the open standards world (SIP) does, but that's the classic codec from 1995 and would definitely be usable on the CPUs of the time; if that's still too slow, then there's always H.261 (1988) which is basically "motion JPEG but with interframes".