Unfortunately this issue persists with the 570.86.16 Beta driver.
Please let me know if I can provide any further information beyond the above perf reports and flamegraphs.
Still stuck using the NGL renderer, which has its own never-resolved nVidia-driver-specific-issues.
With GTK 4.18.x release coming right around the corner next month, it would be great to be able to use the default Vulkan renderer once this issue is addressed.