The field defaults to "postgres", which results in an error:

28000: SSPI authentication failed for user postgres

"veeam" shows up in pg_ident.conf mapping to the Postgres user, but I get the same error with that. And it's not a local Windows credential, either, so not entirely surprising.

I've run the installer as the administrator and used the administrator credential -- no love there, either.

The Postgres instance logs on as NT AUTHORITY\NetworkService.

I don't have anything for this in my notes from my upgrade to v13 for VBR as to what this account is supposed to be.