I remembered I have
Genius Media Pointer E540 for helping in presentations (*khm-khm* when I had such in pre-pandemic times), and it pairs with my Onyx via the USB-C dongle as well
However, there are only a few buttons recognized:
- F5 (the one to the left from the yellow laser button) - acts as screenshot;
- PgUp, PgDn in the middle - works well for turning pages in KOReader;
- The actual "Tab" key with keycode 64 below those - I was able to only assign a single press action in Button Mapper. Maybe I should play with delays for double- and long-press in the Button mapper due to receiver delay, but I didn't test;
- and a key in the bottom right, which interestingly does "Alt, then F4" - so basically refreshes the screen;
- Other keys are "Unknown (0)" in Button Mapper and couldn't be remapped.
Those F5 and F4 also could be reassigned I think, but I didn't try.
This media pointer is from about 2014, so I don't know if it is available anywhere anymore.
However, I think there are much more elegant solutions like
this one, which comes with USB-C right away. If they use something down-to-earth/generic like PgUp, PgDn, etc, this could be very useful.
I *think* Button Mapper does not need root to imitate keycode presses (because I have right now on keycodes and the root-access-granted popup doesn't show), so this might be useful to most of the users.