Partly out of curiosity than anything, I wonder if this would work? I have a 17" MacBook Pro, and the latest version of macOS that it supports is 10.13, High Sierra. It would be interesting to try installing Catalina (10.15) as a guest on Parallels Desktop. I don't think it would violate Apple's terms of service (Catalina would be running on Apple hardware, although on top of a VM), but would Parallels Desktop provide the necessary hooks that Catalina needs? I may download a trial version to give it a try.
@GaryS16 Hi, yes you can install and run Catalina(10.15) as a guest OS using Parallels Desktop 15 for Mac on Host Mac OS High Sierra(10.13). Please try with the trial version of Parallels Desktop for Mac by referring this KB article https://kb.parallels.com/124227
