I am also using a 2018 Mac mini for my Roon Core and have the 6 core i7 version with 32GB RAM and 256GB stupidly quick SSD. Roon playing a 44.1/16 FLAC file to my microRendu takes approx 60% of the CPU of the core which seems very excessive to me…
I have tried toggling wifi and this has no affect. I am using a wired network connection for the microRendu.