I also used many programs on the side and it took me a year to really get comfortable with Roon. I have not regretted paying even a small price for it despite some (pictures) problems. No one finds only friends who always work for you for free
The artist thumbs should probably be artist pictures. It is not always easy with the automatic translations of Google. I use this:
Your Roon Core is at Users/…/AppData/Local/Roon/
It will only be seen if the hidden files and folders are also turned on. This is safer for computer beginners.
There are actually many artists who don’t even upload their pictures to the music services. That’s why every Roon customer is still missing images. With large libraries, you should not tackle everything immediately, but always look for the best and largest image on the side while enjoying music on your own hard drive or on the net. Here images 1920 x 1080 (HD) are certainly the most beautiful. On this occasion one comes then also on sides around many texts to read. Roon offers another form of music enjoyment.
4Hero has 200,000 monthly listeners at the largest music service, but also no artist image.
Afro-Cuban All Stars is not better known, but has a picture on Roon, Spotify and all other services.