Toshiba laptop: empty loader.conf

I’m attempting to install NixOS on an old Toshiba Portege R30-A laptop. Everything seems to work fine up until I reboot, when I get the message No loader found. Configuration files in \loader\entries\*.conf are needed. Repeating the process and looking at the generated loader.conf, it only contains two comment lines.

I’ve run through the GUI installer and selected more-or-less default options, and I’m still seeing this. Having just done that with a NixOS 24.05 USB boot drive, I’ve uploaded the generated /mnt/boot and /mnt/etc/nixos directories to GitHub - me-and/nixos-toshiba-portege-problems in case there’s anything useful there.

Searching around, I did find Bootloader won't install - #5 by stin123 which suggested disabling non-UEFI boot in the BIOS, but that’s not an option on this device: it’ll let me disable UEFI, but there’s no option to disable legacy boot.

Any suggestions for getting this system booting? My current best idea is to bootstrap it to Debian – it has been used successfully with Debian in the past – then try to copy the boot config from Debian onto a NixOS installation, but that seems like a lot of faff!