I saw @Rugby state that one time, but never before or since (though of course I don’t see every post). That was in this post and surprised me so I asked for clarification but didn’t get one. Nor have I ever seen an official Roon statement to this effect.
Obviously I can’t speak for Rugby or anyone else, but lots of people use a fanless case. I have never seen Roon support reject a legitimate software support case because of a fanless case, including my bug reports in Early Access, for instance. The only thing it could possibly affect would be that it runs too hot if the case is not suitable, but that should not happen with a competent fanless case, and it can also happen with a standard case if the fan is dirty. And it would lead to crashes if it does, not software bugs, network issues, or anything else that is a legitimate support case.
Whether the BIOS settings need to be changed surely depends on the cooling capabilities of the case. As I mentioned, the Cirrus7 guys for instance say that the cooling capabilities of their case are better than the standard fan case and mine never gets more than handwarm, so I don’t see what the problem should be.
Edit:
If the fanless case required it, you may have to turn off Turbo in the BIOS, but the case manufacturer should tell you if necessary. That would make its peaks a bit slower, but I don’t see how it would affect Roon operation (and hence supportability). I searched now for Danny posts mentioning fanless, and I found some where turning off Turbo is mentioned, but I found none where it was stated that this would be an unsupported configuration. If it was, surely Roon would say so on the ROCK specification page, one would hope