I have a debian12, with gnome, working properly.
Also I have a MAC, working properly, the latest Xquartz is installed.
When I ssh -X from mac to debian I can open an xterm and it works perfectly.
But when I open an application which needs 3d acceleration it won't work. xlsgears will for example simply stop rotating.
Do you know what is missing from where?

I would suspect bandwidth might be an issue. Encryption isn't instant.

There is a script I have heard of in an Ubuntu context called testssl.sh which might add to your knowledge on the subject.

Most kinds of rendering acceleration require a close linkage between application and video hardware. In other words, the application needs to bypass some things and talk more directly to the hardware. We solved that in virtual space by making a way to allow that more direct communication, or emulating it (albet with a performance penalty).

You are talking down an encrypted channel and the application cannot even DETECT the remote hardware! You are just channeling the X traffic itself. That pretty much either strips out or disables the hardware acceleration.

If there is a way to emulate the hardware and THEN channel the traffic, it MIGHT work. The performance, I expect, would be a drag if it did work. What I would expect is that it would result in more wild and interesting ways to fail, but that might be fun.

it looks like a remote desktop can be a much better way. If I understand well.
Otherwise it is a local home network, the two hosts are actually share the same monitor.

I agree that x11 forwarding is inefficient and takes up a lot of bandwidth with modern graphics. Remote desktop would be the better way. glxgears over x11 forwarding works for me but my older desktop is only an i3...

My first intention was to write something similar but then I realised that OP probably got his fingers twisted in a knot and mistyped a well known glxgears into some excel abomination. And GLX should work - poorly and slowly, but should. Although brief googling shows many tales of woe.

yes, that is glxgears. Anyway, it is working, but extremely slow. In practice no app can be used which requires 3d acceleration.

if you are interested, it was the latest MuseScore 4 appimage.

Also, having done the math, halving the dpi (e.g. 1920x1080 reduced to 960x540) quarters the bandwidth. That might make glxears a little less pathetic.