Usually close to 30 candidates run in the primary. A candidate could get less than 10% and still finish second. Will any serious Republican run?
As many others have said already Kevin Faulconer is already in for 2022. I think he will face Newsom. Newsom's agreeing to sign Calcare into law if it passed has consolidated most of the progressives around him so if a D runs against Newsom it will likely be from the right. The only chance I see of Newsom not facing a republican is if a bunch of Reps gets in like Faulconer Cox Jenner Kiley and Elder again splitting the republican vote and Newsom just gets one serious Dem challenger (IDK Villaraigosa, or Paffrath maybe?) and even then I think it would be hard for them to get like 10% of the vote. So yeah id say the chance Newsom faces a Republican in 2022 is pretty damn high.
EDIT: Just checked Wikipedia and Paffrath is already in for 2022. still doubt he'll get more than 5 points in the open primary lol the only reason he's getting as much support as he is in the recall is he's the only "serious" Dem running in question 2.