IndirectGLX and slow display/redraw


I’m investigating the use of IndirectGLX to display an openGL application using RHEL8 and Nvidia driver 470.129.06.
Machine A runs the application with an export display set to Machine B.
Machine B has IndirectGLX enabled in its xorg configuration.
The result is that the application is slow in its display/redraw.
This can be reproduced with a simple glxgears, so the application is not the culprit.

I tried also on RHEL7 with Nvidia 390.xx and I had the same result.

I don’t have a clear picture of the state of IndirectGLX. I understand it belongs to legacy xorg features, but is it still supported and meant to work ?
What could be the cause for the slowness ? What data or commands can I use to debug this problem ?

Thanks for your help.