Any recommendations on how to use OpenGL from the CLR (.Net/C#) please?

Typically just find bindings for your language and adapt the startup/bootstrap to match your language syntax. Opengl calls are fairly agnostic especially when you move to the shader logic.

The biggest issue with c# dev is OS specific window management. CLR doesn't have good wayland support yet if you're trying to do this from a modern Linux distro.

I can recommend OpenTK [0]. I've used it recently to create a 3D renderer, and I have not run into any issues.

[0] https://opentk.net/