I think you want to make a “headless” setup?
because Roon core has not a GUI, so you can modify, adjust your setup only from your laplet or phone.
In that case I should go for the Ubuntu Server, Check which version Roon recommends, don’t forget to config your server for application optimalisation, because standard Ubuntu server is not set for this, also do minimal install and check other websites for Audiophile Linux optimalisation, because you disable a lot of unnecessary services.
If you want a GUI, just take the Ubuntu destop OS and install Roon on it, this works best op laptops, just plug your USB DAC into it, and off you go.
Both scenarios work with multi room endpoints, and Ropieee DAC’s, personally I don’t hear so much difference between serverless (Roon Core) or complete Roon version, what I do hear is the difference if your music collection is on internal SSD/HD’s or external HD like NAS.
Local storage is much faster, sounds in my opinion better.