The diffs are non-trivial (EDIT: only included changes in directories where conflicts are most likely to occur):

    $ git log --oneline REL_11_2..REL_11_12 -- src/backend src/include ':!src/backend/po' | wc -l
    536
    $ git diff --stat REL_11_2..REL_11_12 -- src/backend src/include ':!src/backend/po' | tail -1
     352 files changed, 14651 insertions(+), 7078 deletions(-)

Even if the conflicts are minor, it's going to be annoying to try to work it out. If you are hitting a specific crash, there's a good chance you can backport the fix cleanly, but I doubt you can just pull in all of the fixes proactively without some knowledge of the details of the fork.

I haven't really looked at the details... perhaps PolarDB already has many (or all) of the fixes since 11.2. Also I haven't actually tried a merge, I'm just assuming the difficulty based on the number of diffs (and my experience doing minor version merges in the past).

(Disclaimer: I work for Citus Data. Citus takes the approach of a pure extension, which means it works on unmodified Postgres, and minor upgrades typically don't interfere at all.)