According to the Arch Wiki, the Linux side is "fairly mature"[0]. The Mesa3D documentation leaves a similar impression regarding OpenGL[1], mentioning that the Linux drivers, including the ones for 3D support, are mainline since 4.4 (released in 2016[2]) with Qemu support since version 2.5 (released around 2015[2]), so I guess, the assessment from the Arch Wiki sounds about right.

The Venus driver for Vulkan is described as "experimental" [4], with Linux kernel side support merged in version 5.16 (release in early 2022[5]).

RedHat is developing VirtIO drivers for Windows[6], but apparently they gave up the work on the OpenGL ICD driver in favor of Vulkan[7]?

That said, I have no clue what the situation on various BSDs looks like. I guess on OpenBSD, this is a first step towards making this chain work?

[0] https://wiki.archlinux.org/title/QEMU/Guest_graphics_acceler...

[1] https://docs.mesa3d.org/drivers/virgl.html

[2] https://kernelnewbies.org/Linux_4.4

[3] https://lists.gnu.org/archive/html/qemu-devel/2015-12/msg027...

[4] https://docs.mesa3d.org/drivers/venus.html

[5] https://kernelnewbies.org/Linux_5.16

[6] https://www.linux-kvm.org/page/WindowsGuestDrivers/Download_...

[7] https://lists.freedesktop.org/archives/virglrenderer-devel/2...