Alpha, Beta, Gold/Master Validation requirments

Dear Ministry of Testing community!

I’m currently working on software oriented validation for different milestones in SDLC.

Want to know if you have great inspirational resources for creating Alpha, Beta, Gold/Master milestones?

Can be anything from blogs, books, videos, podcasts - anything is welcomed! For now would like to focus mainly on functional requirements but non-functional is also greatly appreciated.

Things I’m looking for are i.e. “To be beta software has to have to be feature complete” or “Master can’t have Must/P0/Critical issues present”

The form can be anything! Either specific example or just loose guidelines.

Greatly appreciate and welcome all your input! Even your own examples how your process looked like for such requirements?