Intel made a great thing called CCS (Color Control Surface), however that won't work with kmsvnc. Please set `INTEL_DEBUG=noccs` globally, ideally in /etc/systemd/system.conf.d. Manpage is at `man 5 systemd-system.conf`. For example:
```
# /etc/systemd/system.conf.d/intel-no-ccs.conf
[Manager]
DefaultEnvironment=INTEL_DEBUG=noccs
```
NixOS:
```
systemd.extraConfig = ''
DefaultEnvironment=INTEL_DEBUG=noccs
''
```
If you plan to use the default vaapi driver for Intel and AMD GPUs, please make sure your vaapi configuration is working.