https://bugs.winehq.org/show_bug.cgi?id=56163
--- Comment #6 from C. Leu kle@bluewin.ch --- Many thanks Zeb Figura for the fast hint.
Indeed I had to run "sudo apt install libgl1:i386" and after that the "Failed to load libGL: libGL.so.1" warning is gone.
It is now possible to launch Unigine Sanctuary also via OpenGL but the screen output is totally broken. There are a ton of GLSL warnings displayed and after that the output is just orange and orange-yellow.
This is the stage how it looked on earlier Wine versions when OpenGL was selected. As far as I remember it never worked with pure OpenGL. It worked to some degree via WineD3D and mostly fine on Nine.
See the new attachments for more details.