Inter continues to fight to win the Italian league. That's why they can't play many matches with their reserve squad. Because if they take risks, they also have the risk of losing the Italian league. They have to play every match in the league with the best squad in the match with Napoli. They also have to prepare for the Champions League final. In France, Paris Saint-Germain's job is easier, they have already declared their championship. That's why they can easily put their reserve players on the field in League matches. That's why the French team's players are luckier in terms of rest.
PSG with a title in the hands already have the upper hand in finals, yes as you mentioned Inter need to give it all and win the remaining games because they only need a small mistake from Napoli to overtaken them and win Scudetto this year.
How things turn in Italian championship will have a significant impact on the final, If Inter wins Scudetto they will have a boost in their morale if they don't win the title it will slightly disrupt a delicate morale balance negatively. PSG will be fresher in the final I can bet on that but Inter is a fox team and nobody needs to sing them off. My bets on Inter for now.
In the end, Inter must choose which competition to focus on between Serie A or the Champions League. Inter strength is dominated by old players and physically requires 1 decision to maximize performance. In Serie A, they are 1 point behind and I think Inter still has a chance, but in the Champions League the stakes are 1x and it will be tough if you see PSG condition which is much more prepared. Mentally Inter is clearly better than PSG because they have experience but the stamina to continue breaking down attacks for more than 90 minutes is on PSG side.