So… the steps provided by @Quin_Chou did not work. They left the SSD in a weird state where HW bitlocker was enabled, but the drive would not encrypt. I had forgotten about the BLOCK_SID stuff, it’s been too long - I suspect that not toggling that was what got in the way.
Interestingly, even after a BIOS reset, TPM clear, PSID revert, and secure erase, the BLOCK_SID and SSD security management options are still missing from the BIOS. I’m currently building a Windows 2 Go stick to try enabling HW bitlocker with the instructions I’d previously used here: https://blog.odenthal.cc/content/files/2023/04/Hardware-Encryption-on-a-Samsung-980-PRO-SSD-with-Windows-11-using-Bitlocker.pdf - the example SSD is a Samsung 980 but the directions work the same. I know they work too since I’ve used them on two GPD laptops and a Gigabyte TRX40 motherboard.
The Win2Go stick prep takes forever so I’ll report back with results eventually.