IzzyOnDroid and direct install will install the Proton mail app with Google push notifications. With the main F-Droid repository the maintainers will check the source code. The small team of Tutanota mail app did away with Google in 2018 https://f-droid.org/2018/09/03/replacing-gcm-in-tutanota.html And as far as I know Signal messenger app is available without Google push but using websockets.
IzzyOnDroid and direct install will install the Proton mail app with Google push notifications. With the main F-Droid repository the maintainers will check the source code. The small team of Tutanota mail app did away with Google in 2018 https://f-droid.org/2018/09/03/replacing-gcm-in-tutanota.html And as far as I know Signal messenger app is available without Google push but using websockets.