Look at the partiuuid for your /dev/nvme1n1p1 and compare it to the partuuid of the partition where your endeavouros bootloader (Boot0003) and Windows Boot Manager (Boot0000) are installed.
You mentioned that you had used the ~500 MB partition as ESP for your EnOS and you used Grub. That would be /dev/nvme1n1p4.
However, you have two items for systemd-boot’s bootloader: Boot0001, Boot0004 installed in /dev/nvme1n1p4 (partiuuid 669717d1-91fa-fa42-9595-d480098a6e11).
All in all, it is a bit of a mess 
Myself, I would clean up the whole thing and setup things properly from the scratch.