Hi!
I upgraded Postgresql from version 12.4.3 to version 12.5-3 and
Postgresql reported that "old version of the database format was found".
AFAIK this message usually appears after upgrade between major versions
when there are drastic changes in internal storage format. I now have a
working system back after downgrading the package to 12.4.3.
I am using Arco Linux, an Arch Linux based distribution. Upgrade was
done using package manager pacman. Downgrade was done using cache files
of pacman.
Regards,
Abhijith