Nice awareness. Although I have been using #Disroot as my primary mail service provider since 2018 (just after OpenMailBox was sold), I have recently added #Tuta as a secondary. (Recommendations from fsf.org/resources/webmail-syst…)
Btw, I have been using #K9Mail (becoming #Thunderbird now) since a decade on my Android phone.
I have found that Tuta is not supporting IMAP/SMTP protocols and hence I will have to install Tuta's Android application. How does it works without these protocols?