How would you use this master/dev/feature/release/hotfix to support multiple fielded versions of production software and keeping track of bugs for each? Say you have version 2.1, 2.2, and 2.3 or even 2.0, 3.0, 4.0 and you have to support all.

You may very well have changes that cannot go into /master for all of them. But there could be fixes on foundational code that needs to go into all as separate patch releases.

I have seen some OSS code repos keep the branch, or tag and then branch from the tag for a fix. But implementation of the fix may be a little different in different fielded versions that are production supported releases.