I've just learned that some network cards need to be set into a COMBO
mode for properly booting PXE in UEFI mode.
Here's the log from the FAI irc channel:

07/25/24 [20:25:45] < dpw> My UEFI PXE boot problem is solved: the Intel i350 
network adapters firmware must be flashed in a certain "usage mode" named 
"COMBO".
07/25/24 [20:27:49] < dpw> Unpacking PREBOOT.zip from the "Intel Ethernet 
Connections Boot Utility, Preboot Images, and EFI Drivers" page and unpacking 
PREBOOT.exe within again results in 
                           two files: BOOTUTIL64E.EFI and BootIMG.FLB
07/25/24 [20:29:14] < dpw> Using Legacy BIOS PXE boot, I created an EFI 
partition where I placed those two files, then booted into BIOS again, switched 
to UEFI boot and EFI shell as the 
                           default boot option.
07/25/24 [20:30:13] < dpw> There, a 'BOOTUTIL64E.EFI -NIC=1 -UP=COMBO 
-FILE=BootIMG.FLB' flashed the necessary firmware version on the NICs.
07/25/24 [20:30:51] < dpw> Now the servers PXE boot in UEFI mode.
-- 
regards Thomas

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