In the current situation, Manchester City may have a much better chance of landing Donnarumma than their rivals, because whatever the reason, Donnarumma himself will certainly choose a much better team. Besides playing in the Champions League, Manchester City also offers Donnarumma the opportunity to continue his good form, and Manchester City's great potential to win the Premier League title also makes him attractive. While these aren't the only possible reasons, I see Manchester City's chances as much greater.
The presence of Ederson in Manchester City made the transfer of Donnarumma harder. It is like a domino, just make the move and everything will follow. PSG want him to leave the club but they won't sell him for a cheap price because they will simply wait for the next transfer window in winter to have a better negotiations.