To be able to run Big Sur installer on unsupported mac, you'll need:
- Working Catalina installation
- Patcher
There is two ways to patch it:
- Use my tool, called Big Sur, Please
- Do it manually
You can read more on how to do this in my Big Sur installation guide here: https://medium.com/@andv/how-to-install-big-sur-to-mac-mini-late-2012-9d674b563174