The problem here is, a version of gitlab has been installed higher than it’s actually supporting. The database should have been on 10.x before installing the version that is forcing upgrade to 11.x
12.10.x is attempting to do upgrade to 11.7, but the host is on 9.x so it’s going to fail. 12.0 and higher should have upgraded the 9.x release to 10.x but it seems for some reason that hasn’t happened. Maybe it was disabled, or maybe the upgrade path wasn’t followed correctly to ensure that the upgrade went smoothly, including the postgres upgrades. But impossible to tell without all details.
I think the only way around this is to restore your server to it’s previous version (I presume you have a backup??), and ensure it’s on postgres 10.7 before going any further, and update to 12.10.x once this condition is met, so that it can be upgraded to postgres 11.x in gitlab 12.10.x
In gitlab 13.x postgres 11 only supported (12 is available but optional will be forced in gitlab 14.x), so the 12.x releases had to be on postgres 10 prior to upgrade.