This article mentions that Proton is building custom versions of their apps for a device / android fork that don't rely on Firebase for notifications:
Proton and Punkt have actually partnered on this device, which includes making specific versions of the Proton apps for MC03 which don’t require access to Google’s Firebase for notifications, meaning they’ll work just fine whether you’re using Google services on the device or not.
I could care less about Punkt or AphyOS. Proton without Firebase would be great though.
If these Proton apps are exclusive to the device, any reason why these couldn't be ported?
Apologies if cart is coming before horse here.