You’re post is full of misconceptions and mistakes.

Mail is stored e2ee exculsively. The’ve been summoned to hand over mail many times, which they weren’t able to do. Quick search on Ecosia and find the articles.

They don’t have a master key or else the whole e2ee story is a fad, which it isn’t. The Proton code is in Github so you can check how it works yourself. Part of the password is used to decrypt the data.

Search is done client side. You have to download a big search index in order to have proper search. The iOS app doesn’t support downloading the index so search is limited there.

Please think and do some work before you reply.