There's a Readme.txt file included, that has a list of all the command line options.
No, the Linux version still uses OpenTK and will need "X" to run. Version 3 runs great on a Pi5 - though I've still to test of V4, but that should be better as well.
We hope to have an SD card image that boots directly into ZXNext's OS - that's the goal.
I've updated the Discord link to this one: https://discord.gg/nbZKGPBRKa