If anybody else wants to downgrade to 2.6.3 on from source after upgrading and getting 500 hell, as the Pleroma user and in /opt/pleroma:

MIX_ENV=prod mix ecto.rollback --to 20230504173400 # The error this produces can be disregarded

git reset --hard 7566b4a348c66fcea45bcb017979ece9c7b45b3a # Apparently this is bad in some circumstances but this is what i chose to do

[ run mix deps.get and mix compile, then start pleroma ]