PF2 is definitely NOT "backward compatible" except in the broadest possible terms. You still have Dwarves & Elves, Clerics & Rogues, stats & feats, but the way they are juggled together is totally different. A PF1 stat block doesn't give you anything useable in PF2.
Contrary to Retreater's experience with Forgotten Realms, Paizo's Compatibility licence requires you to completely eschew Golarion lore if you are writing for-profit 3pp content. It's either in a generic world, or in an alternate world of your making. So a prospective module writer can't cuddle up to his favorite location in Cheliax or Nidal, nor expound on the divine virtues of Sarenrae, unless he's willing to make free, not-for-profit material under the Community licence.
This feels like a shame for those in love with Golarion lore. But in a sense it is liberating. It's like going back to the 70s when every DM made up "his own world" out of whole cloth.