Keep in mind that the default way EndeavourOS is set up, it can only detect itself and Windows. Telling by Calamares install logs, it required a coding hurdle to make sure the Windows Boot Manager was shown along with “EndeavourOS Linux”.
This works with GRUB but not sure about the other option: Have to change the “OS_PROBER” flag in “/etc/default/grub”. Someone else will tell you who knows more about it.
@dalto: Thank you. Unfortunately, I do not have a Folder “Ubuntu” in EFI. Can I find that out looking into the Ubuntu-partition? (I can mount the partition).
Unfortunately yes.
Thank you for the link. I do hope that I’ll manage to use the workaround. Your choice of words worries me a bit there…
@dalto: Quick question how can I find the full path of the destination EFI? ubuntus /boot/efi/ is empty… I couldn’t find an EFI file on the partition.
And what is an FS alias?
EDIT:
Finally I got it to work. I booted into Ubuntu where I got the information needed with efibootmgr -v (the path, and the partition FS, Instructions here). Based on those information I was able to find out which FS alias to use.
From there on it was relatively easy to use the instructions provided by you.
The funny thing is: If I now select “Ubuntu” from the boot-menu, I actually jump into GRUB, where I can select Ubuntu or Windows again.