No, I think you are misunderstanding my poor explanation.
Your emails are encrypted at rest on their server regardless if you use the web client or IMAP through the bridge.
The thing is that the encryption layer must happen at some point in time when you communicate with their API:s. In the web client this encryption is built-in. IMAP on the other hand does not support this type of end to end encryption, so the bridge adds this layer for you.
So you communicate unencrypted locally between your email client (Thunderbird for example) and the Protonmail bridge that you have installed locally on your computer. Then Protonmail bridge encrypts and decrypts all emails for you. So to your email client, it seems like a normal email server, but in reality everything is encrypted.
(Standard "encrypted email" disclaimer: Your emails are not encrypted in transit unless both parties, sending and receiving, are set up for encryption. Email is otherwise not end to end encrypted in transit)
This is great news!
Mint is my choice of weapon when it comes to desktop Linux and I have been eyeing the Framework 13 for quite some time now.