Yubikey, but thats just a personal preference. A password manager works just as well.

I just tried to import the OPML file from feeder and it doesn’t seem to work.

It has a great design, which I often find missing from FOSS apps. However I still like Feeder better.

I use both. I have a self hosted docker compose instance of mailcow, which alerts me when an update is available.

I also use protonmail as well.

Self hosting was a pain in the ass to get working, but I’ve had no issues with it once up. I tossed it behind a reverse proxy to keep it from directly touching the internet.