Very interesting insights. Funnily I use all of the services you cautiously recommend, including GrapheneOS, but not HarmonyOS, hard pass on that one. As a German I am also legally required to prefer Tuta. :) I still have that OG 1€/Month contract.

Edit: Your last point is a good idea, although I think the more popular an open source app is, the less likely it is to be malicious. A lot more eyes on it and the xz backdoor was caught pretty much immediately.