Lol when I read a paper that only cites its own work it’s an immediate eye-roll from me. Usually the realm of people who can’t keep their own biases out of their work.

Maybe it’s different for some hyper-specific subfield where no one else is doing anything relevant but I think that’s pretty rare. I don’t know much about physics though. The papers I read are all biology.

My absolute favorite is when there’s two competing camps of researchers who steadfastly refuse to cite the other’s work on a topic. It’s very silly. Citing doesn’t mean you have to agree with all of their conclusions. Not doing so is obstinately refusing to acknowledge relevant data.