How-To Geek wrote a great article about swapping Gmail's app for Thunderbird on Android:
"It's a free, open-source, privacy-focused app, and it makes email feel like it used to."
https://www.howtogeek.com/i-ditched-gmail-for-thunderbird-and-email-feels-perfectly-boring-again/
Check out Thunderbird for Android!
https://sohub.io/npmm