Best to ask for feedback but of course they won't give it to you. I thought I did really well after 6 interviews with a FAANG company. They let me down by saying that another candidate was preferred. I pressed for feedback a month or so later and was ghosted. So I submitted a privacy request to the privacy and legal team about all and any data pertaining to the hiring process and interview, and was given a massive dump of their talent management system, plaintext notes of the interviews, group chat messages discussing me, etc.
It turns out I had a pretty bad read of the situation; there was some things that I had said that were misconstrued, some bad traits that I wasn't aware of, and then the key reason I was rejected (lack of domain exertise and relevant experience).
Anyways glad I went down this route, I still need to process the data and translate it to improving myself, but as my buddy GI Joe says, knowing is half the battle.