if you have terminal that's a plus.
now check if you have internet
ping 188.8.131.52 or
if you have ethernet keep running eopkg nvidia til it sticks, could take a few tries.
if you have bluetooth I don't have any suggestions. I dont use it.
if you have no internet than I suspect problem may be in systemctl services.
looking for a boot menu on booting (F-anything) gives you nothing because boot is destroyed?
I'm throwing everything at the wall that I got. solus boot rescue I wouldn't wish on anyone. sometimes you wake up and the friendship between Linux and Windows on the same disk is destroyed without any hows or whys and thats a fact of life when sharing space, I read about it every day.
what is completely throwing me is you can't move your files in Solus Live because there is no Solus Live thanks to nvidia?
" I tried launching a livedisk of Solus to see if I could at least move my data to a secondary drive to reinstall, but got the same issue I did back when I first installed Solus (no Nvidia drivers)"
so solus live tells you it can't run solus live? like no GUI action at all? Can't access Doflicky?
hopefully you can troubleshoot a little and rule stuff in/rule stuff out. someone at this fine list will step up. getting offline to work for a while. good luck. edit/word
edit #2 look up nomodeset in the search here. I've never had to try it. supposedly a work around with nvidia problem installs but you made it clear you have boot problem and an nvidia I think