K-9 Mail, which will become Thunderbird for Android in the near future, is a popular mobile email client for Android. The app will stick to the original name for now, but will be renamed eventually. New features and improvements will be introduced before that happens to make sure Thunderbird desktop users have a positive user experience.
One of the main issues that users of K-9 Mail ran into was missing OAuth support, as it prevented Gmail from working with the client. Google made OAuth 2 mandatory for Gmail, dropping support for other authentication options.
https://www.ghacks.net/2022/07/08/k-9-mail-future-thunderbird-for-android-adds-oauth-2-0-support/