Hi @admdebian for QEMU/KVM you want the qemu-virgil snap, otherwise you won’t get graphics, the lack of which would explain the EGL errors.
With the above, I can:
snap install mir-kiosk
snap install --beta wpe-webkit-mir-kiosk
and all comes up as expected.
You shouldn’t need --devmode as everything should work confined - those apparmor logs are benign.
As for slowness on X11… I think it may be due to the fact that in that scenario the WPE and Chromium daemons run in the background, and wait for Wayland to become available (i.e. you run mir-kiosk).
If you snap restart wpe-webkit-mir-kiosk right after you start mir-kiosk, does it still take so long to start?
You can see what’s happening with journalctl -u '*mir-kiosk*' -f.
Your Electron snap Just Worked™ for me, too. Just needed to snap connect electron-hello-world-kiosk:wayland if on desktop, and snap restart electron-hello-world-kiosk after mir-kiosk was started.