I had to force Xvnc to start with software GL (glvnd & Mesa GL) because NVIDIA GLX is not supported in VNC by the official driver. This was the only way to enable Epiphany to work within VNC.
Now I have found rendering AND displaying some pages of results at ancestry.com max out the CPU in all 16 threads. The CPU's stay at 100% as the webpage is open.
On the same host, with hardware rendering in X11, Epiphany does not have a problem on those pages.
On Fedora 34, latest Epiphany 40.6 and webkit2gtk3-2.34.1
AMD 5800X and GeForce 9800+ GTX
Some more observations: testing with a page of search results on Ancestry.com. The Developer console says rendering (timeline) is done in 4 seconds and _then_ the CPU cranks up and stays there as long as the results page is open. Showing 10 hits per page vs 50 hits per page does not make much difference. Even when page is just sitting there with no network activity (none in Network of developer console), the CPU's are pegged.
My guess is that each hit has a mouseover pop-up with more details on the hit, and that Epiphany has a problem with the event handler.