maybe your upstream doesn't validate DNSSEC?

maybe? I'm using PiHole and 8.8.8.8/1.1.1.1 as upstream, and both options show "DNSSEC" next to their options in settings, so I assumed DNSSEC was enabled (unless I have to enable this somewhere else as well?)

That's weird cause 8.8.8.8/1.1.1.1 will already answer with SERVFAIL right now, unless the domain is still in the cache.

cache

unlikely, as I have also successfully tried domains that I never visited before (at least not in the last 12 months) and according to my PiHole log they were successfully retrieved from 1.1.1.1. and/or 8.8.8.8, which should use DNSSEC