I don’t have a gitlab account, but this is obviously a bug in pamac.
Based on much feedback from users, when the community repo fails to sync because it no longer exists, pamac does not sync the multilib repo, then it tries to calculate the update anyway. Old versions of packages in multilib conflict with new versions of packages in core and extra. Pamac tries to solve this by removing conflicting packages, but many other packages depend on them. The update fails when pamac cannot resolve package conflicts. This shouldn’t happen because the update should fail as soon as a repo fails to sync.
I have seen so many posts about this in the forum, and the problem always boils down to the fact that they didn’t remove community from their pacman.conf. They completely miss the warning that community failed to sync and only ask about the warning that pamac failed to remove conflicting packages.