In the context of a quiz essay question, at least, the Atto and TinyMCE editors do not play well with Google Gboard on Android 11. The enter key does not move the cursor to the next line, though it does insert a newline into the text editor. This makes it impossible to enter multi-line text. In fact, it appears that nothing is happening when the enter key is pressed. On rare occasion, it will work correctly, but most of the time it does not.
Originally, I thought it was simply the Chrome mobile browser, but I tried Safari and Chrome on iOS and did not see the problem on either of those two browsers. Then out of curiosity, I connected a physical keyboard to my Pixel 4a (5g) phone. Using the physical USB keyboard connected to the phone, the HTML editor works as expected.
I'm on Moodle 3.10.1+ (Build: 20210130) | Version 2020110901.02