I’d say anything that could be considered as creative
This is basically how it’s handled. In the Masterpiece Cake case it wasn’t about selling the couple “just” a cake. If they’d wanted one out of the case the Shop was legally required to sell them one. They wanted a custom cake and that falls under “creative” which changes the rules.
The United States has long held that “Artistic Expression”, basically creative work, is protected under the 1st Amendment as a type of speech and the Government cannot compel speech without extreme need and even then it can only do it narrowly and temporarily.
What we really have with these is a collision between individual rights. Is it fair for the Government to abrogate the 1st Amendment Right of one person by compelling them to speak (create art) in order to satisfy the 14th Amendment Right of another person?
It may seem obvious but consider the controversy around Piss Christ. It was art and was thus subject to 1st Amendment protections and without those protections it would have been removed.