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Virt-Viewer/Virt-Manager has a weird issue when enabling VirtIO video + Spice + OpenGL to enable 3D acceleration. Any Linux guests running on the VM has slow/choppy graphics. In addition window resize does not resize guests if on virtio video. QXL works fine.

Guests confirm virgl acceleration enabled

$ glxinfo | grep OpenGL

OpenGL vendor string: Red Hat
OpenGL renderer string: virgl
OpenGL core profile version string: 4.3 (Core Profile) Mesa 19.3.4
OpenGL core profile shading language version string: 4.30
OpenGL core profile context flags: (none)
OpenGL core profile profile mask: core profile
OpenGL core profile extensions:
OpenGL version string: 3.1 Mesa 19.3.4
OpenGL shading language version string: 1.40
OpenGL context flags: (none)
OpenGL extensions:
OpenGL ES profile version string: OpenGL ES 3.2 Mesa 19.3.4
OpenGL ES profile shading language version string: OpenGL ES GLSL ES 3.20

Host's OpenGL spec (Fedora Workstation 33, Intel UHD 630)

$ glxinfo | grep OpenGL

OpenGL vendor string: Intel
OpenGL renderer string: Mesa Intel(R) UHD Graphics 630 (CFL GT2)
OpenGL core profile version string: 4.6 (Core Profile) Mesa 20.3.4
OpenGL core profile shading language version string: 4.60
OpenGL core profile context flags: (none)
OpenGL core profile profile mask: core profile
OpenGL core profile extensions:
OpenGL version string: 4.6 (Compatibility Profile) Mesa 20.3.4
OpenGL shading language version string: 4.60
OpenGL context flags: (none)
OpenGL profile mask: compatibility profile
OpenGL extensions:
OpenGL ES profile version string: OpenGL ES 3.2 Mesa 20.3.4
OpenGL ES profile shading language version string: OpenGL ES GLSL ES 3.20

However running the VM with QEMU directly with gl=on performs butter smooth.

$ qemu-system-x86_64 -enable-kvm -m 2048 -vga virtio -display gtk,gl=on -cdrom AnyLinuxGuest.iso

Note: This issue does not arise on a cleanly installed Fedora 33 Workstation (non-updated stock iso). It may be regression in recent versions.