Pro micro with USB host shield 2.0. Nate you want 8MHz/3.3v version of pro micro
#Create own USB-USB Host Converter
craggy owl
untold hamlet
untold hamlet
<https://www.adafruit.com/product/5723> with <https://github.com/whyaaronbailey/...
There are other things, e.g. https://nogikes.booth.pm/items/2256612 but that ^ one has the advantage of using a single readily available dev board and not some custom thing or anything you need to put together yourself. RP2040 is much more capable than an AVR Arduino thing too
I don't see why it wouldn't be, but if the other keyboard you're connecting to it doesn't already have that you won't be able to get that with any converter
That should work, but make sure you test key combinations you'd actually need, and modifiers don't count