[webkit-gtk] WebkitGtk 2.26.0 WebKitWebView fails to display in a Gtk3 app.

[jralls at ceridwen.fremont.ca.us]

GnuCash uses a WebKitWebView to display reports that are generated in HTML. Since Michael updated the Gnome41 flatpak runtime to 2.26.0 we've gotten two bug reports complaining that those reports no longer render:
https://bugs.gnucash.org/show_bug.cgi?id=798485
https://bugs.gnucash.org/show_bug.cgi?id=798486

The first one, running on Ubuntu 20.04, failed because of an Windows system error, the second failed because it couldn't find libGL. Both are worked around by setting WEBKIT_DISABLE_COMPOSITING_MODE=1 in the environment before running GnuCash.

Is there a dependency issue here that we need to add libGL to our flatpak manifest, or is it a more basic problem that compositing only works on Gtk4 and that Gtk3 apps embedding WebKitGtk need to disable it? If the latter is that better done with the environment variable or by calling 
  webkit_settings_set_hardware_acceleration_policy (WEBKIT_HARDWARE_ACCELERATION_POLICY_NEVER);
when setting up the embedded WebKit instance?

Regards,
John Ralls