GLX used to work with remote X, what is called indirect rendering, but it sounds like it stopped working recently. Maybe doesn't support recent OpenGL, or nobody uses it so nobody maintains it.
I don't think this has worked well in quite some time. Maybe not ever in open source land.
IMHO, widespread use of Xlib lead people to believe that X was much more synchronous than it is, and discouraged people from using networking, and then a lot of stuff that could be possible didn't get made. xcb is a much better way to interact with X, but it may have arrived too late.
My guess is the lack of shared memory buffers stops the use of opengl, and whilst it's theoretically possible, it is probably unimplemented because nobody does that in 2025.