I’m using a selfhosted pastebin (microbin) as sometimes I want to transfer text, other files… It’s very efficient and in my instance it’s using 13MB of RAM, which is fairly lightweight for modern standards

It’s explained in the FAQ: https://www.beeper.com/faq#how-can-i-self-host-beeper I’ve not used the app so I don’t know how practical/easy it is but they’re at least offering the option, which is laudable.

For what I understood the decryption/encryption process happens on the bridge. The bridge is the selfhosted component so the transformation would happen in your server and they would have no visibility over the unencrypted message.