Personally, I just use it in a web browser for ad-hoc file uploads. If you’re looking for regular syncing though, supposedly rclone works. https://docs.s3drive.app/setup/providers/#usernamepassword-setup
I actually hadn’t noticed it’s not there for mobile, but there’s search in the desktop view of the website
not Foss, Google app warning, don’t shoot me
Google has an app called Reading Mode that you can trigger by holding both volume buttons. Works anywhere and has dictation, but the output isn’t as good as the Firefox one in my experience.