Hi Rudolf.
my 2 cents here
I had the same issue when I used my Synology NAS (916+ model, 8GB RAM). Local library was super fast but Tidal was very slow in search and start.
I got from Roon that some intel processor are just not powerful enough.
The only thing I could do was to move the Core back to my macmini.
HEre is the discussion with Roon team :Roon/Tidal - Synology - #6 by alessandro_niola