[Quoth]

Apps that sensibly use a pen and worth having:
Nebo (also imports PDFs and Nebo files from Kobo). Paid only, worth it for writing and annotating. The handwriting can be converted to a text layer on PDF. PDF can be exported and real text annotation copied off (and separately viewed in Xodo. Also adds an image layer). I bought the pen for Nebo as I'd tried the Apple Pencil on Nebo on the iPad. The Kobo Sage/Elipsa version of Nebo is drastically cut down to suit eink with things like live preview removed. I'll never use the Sage or Elipsa for notes ever again. Not even if battery flat. I have power banks. The iPad has a cut down free version of Nebo. Android has only the paid full version.

Sketch Box Free (some more features on paid version)

Xodo (Free version, no way will I subscribe for ANY software, I'll pay loads if good).

Not so good compared to Nebo is MS One Note. My tame One Note user couldn't believe how much better for shapes and text that Nebo is.

Oddly the Gboard has very good offline handwriting conversion and works as well with a finger tip as a pen. Crazy default settings. Add PC Keyboard & Handwriting and un-select the QWERTY. Turn off all glide except moving finger on spacebar to move cursor. So the Jota text editor or any keyboard input app works great with finger handwriting conversion, without a pen, but not well on eink. The display latency is horrible. Gboard retro-installs on at least as as old as Android 7 instead of horrid ASOP. DO check its theme, glide and PRIVACY (turn off voice and glide and autocorrect and grammar, only have autosuggest).



Decent CAD software on Android isn't as good as stuff on Windows or Linux and is expensive. I don't recommend it.

Snapseed is a simple photo app. It has no setting to differentiate between pen and touch. Not very good, but free.

Not seen any decent sketch apps / photo editing.