Yeah sorry I don’t have a citation handy but I remember hearing interviews with constitutional law experts and scholars in the early days of the Trump presidency that are basically verbatim what I said in my first comment here: “It’s never been tested, but everyone assumes that if a case comes before Scotus, they will rule that the president is immune while carrying out the duties of the office”. All that’s happened recently is Scotus confirmed this assumption. I’m not saying it’s a good thing. Just that it is what most constitutional scholars thought would be the ruling.
It’s why most of the court cases he was battling during his presidency were for things unrelated to his presidency, like his Trump university scam or the Mar A Lago stuff.