Hmm, did you start fresh by removing the prior keys and pacman-keys --init again? (per Arch wiki)
I had likely only used -S for installing what I wanted which worked fine.
(Prior to that I had disabled sig requirements in pacman’s config, but don’t recommend doing that for obvious reasons.)
Yes, that’s what we do, mostly couch co-op daily. Cheaper than new system and get away from horrible Windows.