Rolling back an upgrade basically means restoring your backup from before you started the upgrade work. That's the only procedure.
Thank you Christian. Yup, that makes sense. Unfortunately, we did not take a backup of the repository database, and it looks like it made some changes. That's the reason why I am hoping there is another alternative to downgrade.
That's unfortunate. So probably re-install the old version and use the backed up rpd, webcat etc