> -----Ursprüngliche Nachricht-----
> I think that lives here:
> https://salsa.debian.org/postgresql/postgresql-common
Yes, thanks for the hint. The commit which apparently introduced the change is https://salsa.debian.org/postgresql/postgresql-common/-/commit/d9139f7777a42a39b5b6fabbffc9f020fad4dce5: "debian/maintscripts-functions: Create "main" cluster only when no other clusters exist yet."
Maybe I'm going to ask on the pgsql-pkg-debian mailing list for more details about it, as proposed by Laurenz.
@Adrian, please note that I'm not the one who asked on Stack Overflow, so I'm not cross posting over here. And I definitely am doing an "alongside" installation of two major versions: On my server is installed v16, and now I'm adding v17, as described in my first message.
Thanks again to everybody for your help.
Andy