After reading quite a ton of documentation and videos, I chose an Innuos ZEN mkIIII as new Roon Server. BUT: surprise surprise, in the setup documentation there’s no trace of how to Install Roon Server on the ZEN.
I don’t know if this link is helpful but I had a mini mk1 and installing Roon was simple as per the instructions above, which from memory sound right . Try at your own risk, but I guess you can always reset it.
As far as I know Roon do not approve Innuos as a server but Innuos will say it works and in my experience did work, but honestly switching from an old mk1 mini to a nucleus one was night and day in terms of speed, hangs, no need to regularly restart, etc. I hope the mk3 is better in this regard. I think there are a few happy Innuos users here. Good luck.
I have owned a Zenith MK II, but have bought a Sonic Transport I7 instead. I think it runs Roon better and much faster. I had looked at the new stuff from Innuos, but I think they have become far too expensive and you get more for your money elsewhere