I just learned from Ubisoft support (after asking for a solution for a problem regarding trophies tranferring from the PS4 to the PS5 version of Raibow Six Siege) that not all trophies do carry over. And that the missing trophies have to be unlocked again by playing the game and meeting the requirements. I am struggeling with the "Perfectionist"-Trophy now and I am really mad that I have to unlock it again despite getting it already back on PS4.
The nice person from the support told me that I should post one of my suggestions for improvemen there, because the community managers and the developers of the game take a look at this forum. Afterwards, I was redirected to the Rainbow Six Siege page. Said suggestion is: The developers should make the old requirement for getting the "Perfectionist"-Trophy possible again, as an alternate way to unlock the trophy. That old requirement was getting 3 stars on all the situations.
Like I said, the person from the support was really nice. I suffer from autism and was treated very well. Please, Ubisoft, do something. And thank you.