ZeroCool MotherShipton
So when I add Proton Calendar or Proton Drive this way, the link is indeed to the Proton site where you can download the apks directly.
This method gives me a weird version setup, though. If I look at the Proton Drive app info in Settings, I get the expected version (2.9.0). However, if I look at the version info in Obtainium, I get a string of numbers: 598415131 and the message that "a pseudo-version is in use."
Obviously Obtainium (via that website) was able to add the correct version of Proton Drive. I'm just wondering why the Obtainium app itself lists that strange-looking version number and if there will be any problems going forward.