I know that I cannot access my protonmail email under a wide variety of circumstances that I make efforts to avoid. Two of them involve forgetting complicated passwords, either of which would render my entire (historical) email vault unreadable. But it could absolutely be security theater.

What I have no idea about is Google. Do they even need to do anything targeting you in order to decrypt the data or not? Obviously they can modify your software with a remote update such that they can capture your decryption password, but that's a lot more work than querying a database and using a master key that Google has on hand for this sort of thing.

For Google (and almost every provider that isn't very specifically targeting the highest levels of security at the expense of usability), the answer to the rhetorical question I posed is "yes", which implies that they can read your mail, without having to target you or anything you have.

While (as you correctly pointed out) the fact that you lose access to the data if you lose your passphrase doesn't prove that the data is completely inaccessible without it, the opposite (being able to access the data even if you forget/lose all your secrets/keys) conclusively proves that such access is possible.

> Can you access your e-mail if you lose your phone, forget your password, get a new SIM card, and successfully go through account recovery?

You can't. But this really doesn't answer if there was a special way for law enforcement, which I don't believe there is.

The question was about Google, and there (as with almost any other provider) you can. Most users would be pretty upset (no sarcasm) if something so small (sarcasm) as losing all their means to authenticate actually caused them to lose data.