GitLab-Omnibus: Upgrading underlying operating system (Debian)

We are currently running GitLab on a Debian 10 platform and are planning to upgrade to Debian 11 in the near future. We are using the Omnibus package of GitLab Enterprise Edition and the system is a cluster composed of a PostgreSQL database node, a Redis node, a monitoring node and a few application servers. The user data (repositories, containers etc.) is on NFS volumes.

The GitLab version will not change during the upgrade or at least the change will be relatively minor. We could for example consider upgrading the OS during the same maintenance window when upgrading GitLab from version 14.9 to 14.10.

The official GitLab documentation I could find about operating system upgrades is rather brief:

Can we simply change the paths in both apt sources lists (the main Debian one and the GitLab repository) to point to bullseye instead of buster and do a “apt dist-upgrade”?

Should we change both sources at the same time, or first upgrade Debian and only after that change the sources list of the GitLab packages?

Would you recommend stopping the GitLab service for the duration of the operating system upgrade?

Anything else we should take into consideration?