TrueNAS boot issue on C2550D4I (Marvell SE9172)

For some reason when I run the TrueNAS (CORE) installer, either TrueNAS-13.0-U6.4.iso or TrueNAS-13.3-U1.iso on my box (C2550D4I) I can’t boot from it. I’m installing to an SSD plugged into a SATA port on the Marvell ‘controller’. While this isn’t recommended (BIOS says boot will be slower), all 6 other SATA ports on the main board are dedicated to my storage pool. The thing is, this works fine when I install vanilla FreeBSD (FreeBSD-14.2-RELEASE-amd64-disc1.iso). I don’t know why, but it does… When I install TrueNAS, I can’t see the option to boot from this drive in the bios. I don’t change bios settings between OS versions.

I’m installing as UEFI boot. I think I tried ‘BIOS boot’, but I had the same issue. Not 100% sure.

Is there some way I can ‘dual boot’ TrueNAS on top of the FreeBSD?

Sorry if this is a stupid question.

My ‘plan B’ is to look at how FreeBSD does the disk partition and see if I can recreate that after installing TrueNAS. My plan C is to stick with FreeBSD ;-p

Many thanks for any tips.