I don't doubt that he will play at some point in 2021 because rare is the NFL QB who starts and finishes every single game.
If Fields starts ahead of a healthy Dalton, at any point of the season, then that's a pretty costly backup QB that the Bears just signed. If they really think that Fields will work his way into the starting role in his rookie season, then why sign Dalton to a one year $10MM deal and pay dearly in draft choices for a QB who just turned 22 and has never taken a snap in the league ? If that's the case, then they should have kept Trubisky and saved themselves $7.5MM (the difference between Dalton's and Trubisky's 2021 salaries).
I gotta believe they try and release/trade Foles and his salary if they can.