I don’t see if you have a NVMe drive or normal HDD/SSD drive, so my suggestion would be to first locate the EFI boot partition like in:
In that post, it is a NVMe drive (/dev/nvme0n1) and the EFI partition is the first partition (-p 1)
efibootmgr -c -d /dev/nvme0n1 -p 1 -L "QUBES" -l '\EFI\qubes\grubx64.efi'
Had it been a SSD (eg. /dev/sdb) and partition 2 (-p 2), then I guess command should be something like:
efibootmgr -c -d /dev/sdb -p 2 -L "QUBES" -l '\EFI\qubes\grubx64.efi'
Disclamer: I’ve not tested that, since I don’t have Qubes on a SSD
As @szz9pza wrote: I you want a title with one/more space in, put "s around the title.