Where is macOS's incompatible apps blacklist stored?
On Catalina, the incompatible apps are likely determined programmatically when they reference any 32 bit libraries, so that’s an easy check. During installation and migration, the package that contains the blacklist is downloaded:


When I upgrade from 10.12 to 10.13 High Sierra - where do incompatible items go?


I’m not finding any remnants of that file left around - com.apple.pkg.CompatibilityUpdate but you can see things that are moved to the Incompatible Software folder at the root.

Also, for Catalina, there are efforts to package just enough libraries to run old favorite apps even though Apple isn’t shipping the libraries needed.


https://tidbits.com/2019/09/18/moving-to-catalina-keep-your-32-bit-mac-apps-running-with-parallels/
https://www.parallels.com/blogs/catalina-32-bit-apps/
https://www.dpreview.com/news/1439854984/this-app-can-modify-aperture-and-iphoto-so-they-will-continue-to-work-with-macos-catalina
https://github.com/cormiertyshawn895/Retroactive


Since Retrocative is open source, there’s hope interested people can log apps they want, contribute or fund people that are able to generate the code needed for preserving vintage bits on more modern OS.