Alcaraz is not finished yet, he is still WN 2, don't become discouraged from the QF loss to Zverev, but he must improve if he desires to win more slams and come close to stopping Novak at any future slams.
In terms of total slams for Novak I think he will get 27, maybe 28. He had so much to prove and so much to play for last year. This year and going forward he has much less to prove, apart from more of the same. His body is getting older and he will inevitably slow down.
I am predicting that next year Novak will start slowing down as age starts to catch up to him and younger players such as Sinner, Alcaraz and Rune will have become much better at their game and will improve greatly and they will take slams away from Novak, it may not happen this year.