So, what you are saying is that you are running Roon OS and Roon Server on the NUC, NOT Windows?
Show a screen shot of your ROCK GUI web configuration page, please.
And, then i assume you are running Roon also on a Windows machine? Because %localappdata% is a windows only shell folder…
Still, you won’t find anything in the Server-folder on the device only acting as a remote. The server part of Roon is running on the ROCK device.
Still, running a 400K track library on a NUC will be slow as molasses. While i agree there has been performance hits for these older NUC’s with the latest Roon release, you are pulling a huge load with a moped engine… Get yourself a proper server computer, no need for extreme things, but a desktop/workstation CPU with a relatively low Core count and high frequency is best suited.
You can have a look at the first posts of this thread regarding a similar behaviour. And also get info on what cpus and config might suit your needs…