You can use it without 4k or HDR input signal. Simply turn off HDR to SDR tone mapping in the grabber configuration as probably you wont need it.
There some significant changes mainly in v4l2 grabber (grabber's process capture optimization, support for multi-threading instead single thread in Hyperion.NG, YUV/HDR tone mapping), color transformation (color calibration, extended image to LED color transformation) and it's targeted for newer Debian Buster so you can test it how it works for you.
And support for USB grabbers in Windows is coming
Great! I'll try it out soon! Thank you, my friend!