Yes, the dependency chain is a bit unfortunate when you want to solely install an older-than-latest version of PostgreSQL, because e.g. postgresql11 REQUIRES postgresql which in turn RECOMMENDS postgresql12 (or whatever is the latest version we have packaged). Maybe I should consider lowering that RECOMMENDS to a SUGGESTS next time I make some bigger changes to these packages anyway, e.g. when introducing version 13 in a few weeks.