Mechanically, Pathfinder 2e is a completely different system. Even the things that share the same name are different enough that you can use basically nothing from 3.5e or Pathfinder beyond the ideas themselves—all the numbers, effects, conditions, costs, and so on are going to have to be redesigned from scratch for 2e.
Narratively, Pathfinder 2e has officially made Golarion the default setting, for better or worse, and of course it roughly captures a similar kind of magical fantasy world to those Pathfinder 1e was best suited to representing. So any narrative descriptions of setting content—particularly Golarion, but also really any other D&D setting—can be used with 2e about as well as they can with their original systems.