Upon flashing a new image to my motherboard something went wrong. My UEFI boot entries were gone and thus I was not able to boot anymore. In order to fix this I manually added a boot entry again and here’s how to do it.
First boot any live Linux. I recommend a live image of the latest version of Ubuntu LTS for this purpose, but any live Linux will do.
Then recreate a UEFI boot entry like this:
You will now see the new boot order. You may want to change the boot order like so: