Things seems to be going backwards in this area..
[1] https://code.qt.io/cgit/qt/qtbase.git/tree/src/plugins/platf...
We also have a homemade documentation system, again outdated but certified. I don't remember the system but it is definitely not a modern Linux. I think there is also a Fortran tool used to compute the lifespan of parts on the same system.
A bit more recent, we have test benches made of several computers, mostly Linux desktops, each one deal with different things like real or simulated avionic hardware, they can be remote controlled but some apps run locally and have their own displays.
We also have certified build chains running on specific systems, and while a GUI is typically not needed. It may be useful from time to time, mostly for debugging.
We are in a process of modernizing all that stuff, but because of certification and the average lifespan of a program, it is a very slow process...
X11 forwarding works with the latest Linux distros as well a 20+ year old systems running motif apps. Note: the old systems are now virtualized but we still need them, I work in the aeronautic industry and these are the time scales we are working with.
I don't know of any replacement, at least not one with that level of adoption. Again, we really want to run graphical applications on a server, not a remote desktop.
And BTW, things are getting troublesome. More and more Linux apps integrate accelerated web browser components and these tend not to play well with X11 forwarding.
Love the irony of using a remote display to show an Electron app BTW.