It's interesting as typeface plagiarism became rampant beginning in the 70s when more accurate photo reproductions made it trivial. This was problematic for designers wanting to make a livelihood, which is something ITC sought to mitigate by better up-front payments (IIRC from U&lc's coverage) to incentivize quality typeface creation.
There's a distinction though between literal plagiarism and just inspiration from elements. US copyright law doesn't protect either for typeface forms but ironically it does allow copyright for the code used in font files.
I've seen OpenAI's o3-mini (their reasoning model) suggest verbatim code and comments that I found on Github predating LLMs by years. It seems the more times the same code and comment appears online the more likely this is to occur. I'd imagine there would be studies looking into the scope and frequency this occurs and how much is considered fair use.