Btw, most emails are not end to end encrypted on proton. Only emails from/to other proton users or emails sent/received using their “password-protected emails” feature and of course any emails sent/received from anyone that’s using openPGP.

I know that, but I'm talking about the emails that are stored in your inbox, not incoming/outgoing messages.

Also the free tier only includes 500 MB of storage which is extremely little

I've been using Proton Mail since 2020 and so far I only used ~100MB.

it also doesn’t include IMAP support

Because it's impossible to offer IMAP when all the messages are encrypted. They would have to decrypt your messages on their servers in order to allow you to connect via IMAP. Proton Mail offers a workaround though, you can download their Proton Mail Bridge application on your computer, which will locally decrypt the messages and create a local IMAP server that you can connect to with your Email client of choice. That way, the unencrypted messages never leave your computer.

it also injects ads into your sent emails which is stupid

Uh, no. Where does Proton Mail inject ads? That's only something that Google would do. If you mean the signature, Apple has been doing the same thing for over a decade. It's not really ads though, it's just a short string of text saying 'Sent from Proton Mail'. It's added before the message is sent though, so you can just delete it. Apple does the same thing, if you send an email from an iPhone it will say 'Sent from my iPhone' in the Email signature.