Now booting as normal so this is what I have:-
alastair@ibmserver3:~> lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 5.5T 0 disk
├─sda1 8:1 0 500M 0 part /boot/efi
├─sda2 8:2 0 2G 0 part /boot
└─sda3 8:3 0 5.5T 0 part /multimedia
sdb 8:16 1 28.9G 0 disk
├─sdb1 8:17 1 500M 0 part
└─sdb2 8:18 1 2G 0 part
sr0 11:0 1 943.4M 0 rom
sr1 11:1 1 1024M 0 rom
nvme0n1 259:0 0 1.8T 0 disk
└─nvme0n1p1 259:1 0 1.8T 0 part /var
alastair@ibmserver3:~>
Boot order is strange but works:-
alastair@ibmserver3:~> sudo efibootmgr -v
[sudo] password for root:
BootCurrent: 0007
Timeout: 10 seconds
BootOrder: 0007,0001,0002,0003,0004,0005,0006,0000,0008,0009,000A,000B,000C,000E
Boot0000* CD/DVD Rom PciRoot(0x0)/Pci(0x1f,0x2)/Ata(0,0,0)/CDROM(1,0x740e0,0x7800)
Boot0001* Floppy Disk VenMedia(0c588db8-6af4-11dd-a992-00197d890238,00)
Boot0002* Hard Disk 0 VenMedia(0c588db8-6af4-11dd-a992-00197d890238,08)
Boot0003* PXE Network PciRoot(0x0)/Pci(0x1,0x0)/Pci(0x0,0x0)/MAC(3440b592a054,0)/IPv4(0.0.0.00.0.0.0,0,0)
Boot0004* Hard Disk 1 VenMedia(0c588db8-6af4-11dd-a992-00197d890238,09)
Boot0005* Hard Disk 2 VenMedia(0c588db8-6af4-11dd-a992-00197d890238,0a)
Boot0006* Hard Disk 3 VenMedia(0c588db8-6af4-11dd-a992-00197d890238,0b)
Boot0007* opensuse HD(1,GPT,bb17f2bd-67b7-41b2-9527-19d1beca5cb2,0x800,0xfa000)/File(\EFI\opensuse\grubx64.efi)
Boot0008* Diagnostics VenMedia(0c588db8-6af4-11dd-a992-00197d890238,da)
Boot0009* iSCSI VenMedia(0c588db8-6af4-11dd-a992-00197d890238,04)
Boot000A* iSCSI Critical VenMedia(0c588db8-6af4-11dd-a992-00197d890238,05)
Boot000B* Legacy Only VenMedia(0c588db8-6af4-11dd-a992-00197d890238,ee)
Boot000C* Embedded Hypervisor VenMedia(0c588db8-6af4-11dd-a992-00197d890238,01)
Boot000E* USB Storage PciRoot(0x0)/Pci(0x1a,0x7)/USB(0,0)/HD(2,GPT,21800a4c-ab06-4d3c-a1c4-619a3eaf4a31,0xfa800,0x400000)
alastair@ibmserver3:~>
I have no idea what all the VenMedia UUIDs are about and I had no sight of the 500 MB FAT partition which contains the EFI partition. In other words I am not conscious of copying it from the USB to /dev/sda1. It just appeared there after I had done everything else and rebooted.