It appears that the rendering fallback was triggered correctly, but there is a rendering error.
I haven't enabled window transparency, but:

Expected scene:

It appears that the rendering fallback was triggered correctly, but there is a rendering error.

Does OpenGL normally work on your VM if you explicitly switch to it without invoking any fallback? Please try both master branch and this PR.

Seems to be working as expected, but I tested it only on systems with D3D12 support (by breaking various checks). Ideally, it should also be tested on old hardware w/o D3D12 support, in case something is failing in an unexpected way.

I actually have an old laptop with an Intel GPU that supports neither D3D12 or Vulkan, I'll be testing the PR on it.

For the reference, I have tested only DX→Vulkan fallback.

For fully reliable fallback to OpenGL we might need a full engine restart. Some OpenGL drivers can crash if Vulkan content was used in the same process (#103518, #101659).

Does OpenGL normally work on your VM if you explicitly switch to it without invoking any fallback? Please try both master branch and this PR.

Using --rendering-driver opengl3 allows the display to function properly.

Supplement, #112293 can normally trigger rendering fallback and display the screen.

Figured the reason for the transparent window. When D3D12 is attempted first, the window gets created with the WS_EX_NOREDIRECTIONBITMAP flag.

The flag gets removed on the next style change after the fallback, but this doesn't seem to be something that works consistently. It works on my PC, but doesn't on a VM or the old laptop I just tried. See: https://stackoverflow.com/questions/40576394/setwindowlong-with-gwl-exstyle-and-ws-ex-noredirectionbitmap

This may require recreating the window without the flag. So, I should probably tackle this only after the following PR gets merged first: #112344

I've rewritten the RD device initialization code and made it recreate the window if the "no redirection bitmap" flag needs to change, it all works fine on my end now.

I've rewritten the RD device initialization code and made it recreate the window if the "no redirection bitmap" flag needs to change, it all works fine on my end now.

Me too.

Thanks!

@blueskythlikesclouds

Another user has reported a d3d12 error to me. Is there a way to make this trigger a fallback as well?

That appears to be a D3D12 implementation bug, not something that would require falling back to Vulkan. Please confirm that the user's drivers are up to date. If they are, and this problem still happens, you should open a new issue.

It would be useful if you could compile a build with this macro set to 1, and make the user run it with the --gpu-validation command-line option. It will likely print useful information.

I think that DX12 buffer issue is already reported to Godot repo