I think I saw that Proton said in 2020 that the Proton Mail app would come to F-Droid. Sadly I cannot find that information any more. I thought about deleting my Proton mail account today but before doing so ask here about the state of a possible F-Droid app. Yes, I could ask the Proton people, and could also ask the F-Droid forum people but Lemmy feels most comfortable right now.