I'm clearly a Jones denier but I'm not sure about the backup gig.
I count PIT, NYJ, CLE, LVR and NYG as clearly looking for a QB next year. Possibly NO and LAR if they're looking to cut their vets and restart, and less likely IND, TEN and CAR if they want to move on from Richardson, Levis or Young. And that's not accounting for anyone getting injured between now and next September.
It looks like there may only be two draft eligible QBs who are worthy of going in the 1st round and could possibly start week 1.
Then looking at free agents to fill those holes, I have Darnold and Russell Wilson as getting starting jobs (possibly re-signing with their current clubs) then Derrick Carr and Matt Stafford if their teams move on. Aaron Rodgers likely gets a job (possibly undeservedly) as well if he continues playing.
So my math says at minimum two and most likely three or more jobs are open for very undesirable QBs and the free agent field is Jameis Winston, Justin Fields, Joe Flacco, Gardner Minshew, Andy Dalton and Daniel Jones. I think the odds are better than not that Jones lands as a starter somewhere as I'd guess most teams would see him as 1st or 2nd amongst this list of less desirable QBs.