A Honda Civic from 15 years ago was a great product and will get you to point A to B and every parking garage supports it, but if you are having problems today with your old car, you don’t go buy that 15 year old Honda.
My words are saying the NUC line works very nicely with Roon, but a “120EUR” investment into a 6-7 year old machine might result in getting what you paid for. I hope there wasn’t an SSD included in that – or a spinning drive. The spinning drive is against the suggested hardware, and an SSD that old is bound for failure.
All that said, I believe your real problem is with WiFi – unfortunately, you picked a NUC that we did support WiFi on… but if you use the WiFi on it, caveat emptor.
Give it a shot, it may work well… but it’s not the one I would have picked, especially in a fanless case.