I have an old BIOS server for test purposes. It has 8 Gb physical RAM.
Yes, it's not much, but serves well for some small testings.
Applying the script to a PVE 6.0 ISO results in an initrd of 760 Mb size. Booting this in the BIOS server with linux/initrd and the same parameters as your config gives no problems.
Applying the script to PVE 6.2 ISO gives initrd of 880 Mb size. Plain linux/initrd give "error: the initrd is too big" and kernel panic. The 120 Mb increase in size made a difference in the booting I still cannot explain.
So I tested in another UEFI server, first leaving it with same 8 Gb RAM.
Plain linux/initrd give same error. Using linuxefi/initrdefi solves the problem *for some strange reason* I cannot explain.
But I cannot use linuxefi/initrdefi in the old BIOS server.
Now, I have no idea how long will last the global possibility of still needing to install to legacy BIOS servers; I think Proxmox team still support this for some good reason. But if Proxmox team suddenly said "BIOS too old, we're no longer supporting it", then I'd shut up once and for all and simply stick with linuxefi/initrdefi for good.
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