Welcome to the forum, @ADONIOU_SOTIRIS! Unfortunately, it isn’t possible to return to a previous state unless you can restore a previous version from a system backup.
It’s very possible and why you guys don’t let it be is beyond me. if you have an older version of Roon possible in your downloads. Back up Roon
uninstall roon save data option then install older version
if you can’t see library try to restore from backup. If this fails due Roon gods making sure all past is bad just rescan
dear Roon stop playing god let us mortals have fun too.
@Henry_McLeod and I are community members and do not represent Roon. We are simply stating what is or is not possible. Roon has a rolling release policy, so will only ever publish the current version.