caos

That’s a good starter list. However it should be noted that all the Simple apps should be avoided now and instead people should use the forked versions from Fossify.

Yes, that’s right, all the recommendation lists are no longer up to date in this respect. However, until all Fossify apps have been released, the Simple apps from F-Droid can still be used. They have no ads, they are just no longer updated for two months/the time of sale…

Here is a very good collection of Foss apps for Android “40+ Best Open Source Android Apps” by itsfoss.com (almost all available in F-Droid)

Yes! Ghost Commander is open source and it’s able to transfer via sftp

FairEmail is also recommended by many. It has even more functions, but is therefore also a bit more complicated.

for Android: k9-Mail