Hacker's Keyboard (official). Contribute to klausw/hackerskeyboard development by creating an account on GitHub.
I know it's on F-Droid but it is very old. I try using Obtainium, but there's no apk for it on GitHub. Not sure it would even work on latest GrapheneOS.
Anything similar in free/libre?
GitHub blurb mentions "WARNING: This is a rather ancient project that was originally developed back in 2011 based on the Android 2.3 (Gingerbread) AOSP keyboard. While it still works as-is for many users, it would need some major rewrites to work with newer APIs, and some features such as language switching or popup keys don't work right on modern Android systems. I'm not currently planning on significant updates, and it's possible that it will stop working on modern devices or will no longer be updateable via the Google Play store due to minimum API level requirements. Play Store requires targeting API level 29 (Android 10), while the code was written for API level 9 (Android 2.3) from 2011." and I thought I saw that the F-Droid package is 7 years old.
From my own research, it looks like nothing else with commensurate features have been worked on for the past decade. There is no alternative keyboard that supports Function Keys built-in
Yes, I've also gone back to Hacker's Keyboard on GrapheneOS (been using it on LineageOS for years) after checking out some alternatives.
Interestingly enough, my new Pixel Tablet's screen has less contrast than my trusty old AMOLED on my Samsung Tablet.