I’ve added the modules and updated the initramfs as the Chrultrabook post-install docs instructed (even updated the kernel to 6.16.3, just in case), but my Hyperdrive port replicator and DisplayPort monitors are still inert.
Operating System is Debian 13, firmware is MrChromebox’s UEFI Full Rom.
I successfully tested DisplayPort over USB-C on Ultramarine Linux, so it’s clearly an OS-level thing.
Chrultrabook’s hardware compatibility chart mentions that TB/USB4 requires some systemd service, but the setup and post-install guides don’t mention it.