Cam was here in 2020 because the Pats were in a really tough spot capwise and so there were no good alternatives available. And it was obvious to all that Belichick trusted Newton more than he trusted either Hoyer or Stidham to run the offense.
I do think going into this year, Belichick took into account all of the issues from last year that have been well documented: lack of training camp, limited practice time, serious holes in the roster, and a bout of CoVid that may have been more serious than what the team or Newton revealed. It's also telling that Newton was signed to a one year, incentive-laden contract, and the Pats drafted a QB in the first round.
Newton will probably be better than the #30th ranked QB in 2021. However, I don't think Bill or anyone else sees him as the probable long term answer. I do think he thinks the roster is much improved (I completely fail to see the Volin-like arguments that it's not), and so Bill is not opposed to running it back w/ Cam after a much more normal offseason and training camp, while giving Mac time to actually learn the nuances of NFL offenses and defenses.
Cam is the starter now, and will almost certainly be the Week 1 starter. And after that, it will take two things to change the situation, barring injury: (a) Cam is so bad that the team is losing games that they could have won with a league average QB; and (b) Mac Jones shows enough in practice that he is able to take the field and improve the situation. Remember that the Patriots do not believe in the concept of "game day player", and that will never change, nor should it, so (b) will be important if we don't want to see Brian Hoyer take the starter's snaps.