Hi Everyone,
It should be safe to upgrade MacOS if you so desire.
Turned out it wasn't that MacOS 26 broke opengl, so much as it broke Hardware acceleration inside a VM, which is where I was doing the development. So long story short, it probably always worked on MacOS 26, but that wasn't visible to me.
This may be indicative of Apple's direction of travel though, so I'll keep an eye on future versions of MacOS as they come out.
Peter.