Well, obviously Windows drivers are not needed everywhere because obviously they are not needed on macOS. The onboard USB drivers of Windows seem particularly limited in general, so many devices come with their own additional drivers. (Or at least this was the situation in the past. The Rega manual speaks about Windows 7 and Vista … it may be different today and Windows 10/11 may even work with built-in drivers)
It simply depends on whether the onboard driver is sufficient (like on macOS) or not (like on Windows). The situation with the Linux-based OS in the Nucleus might be like with macOS (does not need special drivers) or like Windows. Since Rega says nothing about Linux, you’d have to try.
Like @BlackJack already said repeatedly, post screenshots of what you see.
Does the Rega have an HDMI input? Then it probably works. You’d have to try (and an HDMI cable is a few euros).
Edit: As per the manual posted by BlackJack, there is no HDMI input on the Rega, so no
It would be up to Rega to write what it works with. Roon can’t test and write instructions for every DAC on the planet. There are the Roon Tested and Roon Ready certification programs for this.
I don’t know, did you search the forum?
Edit: A Rega Saturn worked with a Nucleus here:
and here (same user):
However, there were no problems with this, so nothing else was said. Maybe @James_Knapman who opened these threads is around and can tell you what you have to choose in the Roon Audio settings for the Rega Saturn DAC to work.