Efibootmgr cant remove old OS entry

I realise this is more of a generic Linux question & not directly Manjaro, but Im hoping you can help regardless as it’s so hard to find good advice. I will be using Manjaro to complete this task.

I recently replaced Ubuntu with Nitrux on a 2nd partition. Now when I enter the UEFI bootmanager screen (F12) I can still see Ubuntu as well as Manjaro & Nitrux.

I removed this entry using sudo efibootmgr -b 0003 -B & it was apparently successful. However, after a reboot this entry was back again.
How should I get the removal to persist?

efibootmgr -v                                                    ✔ 
BootCurrent: 0000
Timeout: 0 seconds
BootOrder: 0000,0005,0003,2001,2002,2003
Boot0000* manjaro	HD(1,GPT,b81116c0-132d-4850-aa2a-0aa263bea0df,0x800,0x100000)/File(\EFI\manjaro\grubx64.efi)
Boot0001* EFI PXE 0 for IPv4 (7C-8A-E1-80-E5-AB) 	PciRoot(0x0)/Pci(0x2,0x3)/Pci(0x0,0x0)/MAC(7c8ae180e5ab,0)/IPv4(0.0.0.00.0.0.0,0,0)RC
Boot0002* EFI PXE 0 for IPv6 (7C-8A-E1-80-E5-AB) 	PciRoot(0x0)/Pci(0x2,0x3)/Pci(0x0,0x0)/MAC(7c8ae180e5ab,0)/IPv6([::]:<->[::]:,0,0)RC
Boot0003* ubuntu	HD(1,GPT,b81116c0-132d-4850-aa2a-0aa263bea0df,0x800,0x100000)/File(\EFI\ubuntu\shimx64.efi)RC
Boot0005* Nitrux	HD(1,GPT,b81116c0-132d-4850-aa2a-0aa263bea0df,0x800,0x100000)/File(\EFI\Nitrux\shimx64.efi)
Boot2001* EFI USB Device	RC
Boot2002* EFI DVD/CDROM	RC
Boot2003* EFI Network	RC

Did you check the bootmanager in the “BIOS” of your computer? Maybe there you can remove the entry permanently.

The BIOS does have an EFI section but it only allows me to re-order them.

I believe you have to put the number in twice

sudo efibootmgr -b 0003 -B 0003

man efibootmgr entry gives a use example:

Deleting a boot option
Assuming the configuration in the first example, efibootmgr -b 4 -B
could be called to delete entry 4 and remove it from the BootOrder.

I have tried both 3 & 0003 & in both cases it is deleted but it returns after a reboot.

efibootmgr -v                                        ✔  18m 48s  
BootCurrent: 0000
Timeout: 0 seconds
BootOrder: 0000,0005,0003,2001,2002,2003
Boot0000* manjaro	HD(1,GPT,b81116c0-132d-4850-aa2a-0aa263bea0df,0x800,0x100000)/File(\EFI\manjaro\grubx64.efi)
Boot0001* EFI PXE 0 for IPv4 (7C-8A-E1-80-E5-AB) 	PciRoot(0x0)/Pci(0x2,0x3)/Pci(0x0,0x0)/MAC(7c8ae180e5ab,0)/IPv4(0.0.0.00.0.0.0,0,0)RC
Boot0002* EFI PXE 0 for IPv6 (7C-8A-E1-80-E5-AB) 	PciRoot(0x0)/Pci(0x2,0x3)/Pci(0x0,0x0)/MAC(7c8ae180e5ab,0)/IPv6([::]:<->[::]:,0,0)RC
Boot0003* ubuntu	HD(1,GPT,b81116c0-132d-4850-aa2a-0aa263bea0df,0x800,0x100000)/File(\EFI\ubuntu\shimx64.efi)RC
Boot0005* Nitrux	HD(1,GPT,b81116c0-132d-4850-aa2a-0aa263bea0df,0x800,0x100000)/File(\EFI\Nitrux\shimx64.efi)
Boot2001* EFI USB Device	RC
Boot2002* EFI DVD/CDROM	RC
Boot2003* EFI Network	RC

    ~  sudo efibootmgr -b 3 -B                                          ✔ 
[sudo] password for rico: 
BootCurrent: 0000
Timeout: 0 seconds
BootOrder: 0000,0005,2001,2002,2003
Boot0000* manjaro
Boot0001* EFI PXE 0 for IPv4 (7C-8A-E1-80-E5-AB) 
Boot0002* EFI PXE 0 for IPv6 (7C-8A-E1-80-E5-AB) 
Boot0005* Nitrux
Boot2001* EFI USB Device
Boot2002* EFI DVD/CDROM
Boot2003* EFI Network

Boot0003 returns after a reboot