To do so:
- Before the configured timeout, press the arrow down key to navigate to “Advanced options for Qubes (with Xen hypervisor)” & press enter to choose.
+
- Press the arrow down key to navigate to “Xen hypervisor, version 4.x.x.config” & press enter to choose.
+
- Arrow down to navigate to the last known good config & press enter to choose.
+
If all goes well and, you’re able to boot/login as expected; take a breathe, have a laugh and begin backing up your qubes.
Hoping this helps. 