It is a custom ROM(Firmware). @superceleron is a firmware developer from Freaktab with a nice touch for improving the stability, features and performance over stock firmware. He is also a member of this forum.
The ROM of his I have used is not based on the firmware that Khadas just released.
I do not know if he plans a ROM based on the latest firmware, but his last ROM is pretty nice.
Custom ROMs are flashed to the VIM3 in the same manner Khadas firmware is flashed. Same tool is used to flash his ROM images.
He also often does Android TV ROMs as well, but in your use case, his regular Android is probably better suited to your needs.
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