of course Haaland's physique has begun to decline because he spends more performance in the EPL which causes his performance in the champions league to decline. that is the reason some coaches will keep reliable players in the premier league like Real Madrid not too focused in La Liga for a strong performance in the champions league but the results are still bad.
so Haaland might need a little rest to improve his performance in the final later. even though Inter Milan is not too strong but usually Inter Milan can suddenly improve its performance and Man City must be ready to face attacks from Inter Milan.
Haaland is not the only player that plays consistently. Other players like De Bruyne also have a tight schedule like him. Haaland is young and can withstand the amount of games and he is also motivated to keep breaking records. I just noticed that he was just not lucky in the game against Real Madrid. Haaland had a relatively good performance and made two clear goal attempts that would have been difficult for any goalkeeper to save if not for the quality of Thibaut Courtois. One of the shots was punched by the Belgian and it still hit the goalpost. It is not compulsory that he must get a goal in all games, what matter is that the won the game.