After learning Apple killed off FireWire (IEEE 1394) support in macOS 26 Tahoe, I started looking at alternatives for old FireWire equipment like hard drives, DV cameras, and A/V gear.
I own an old Canon GL1 camera, with a 'DV' port. I could plug that into an old Mac (like the dual G4 MDD above) with FireWire—or even a modern Mac running macOS < 26, with some dongles—and transfer digital video footage between the camera and an application like Final Cut Pro.
Apparently one can get firewire via Thunderbolt-3(?) to Thunderbolt-2 to Firewire. It takes cobbling two Apple adapters together to down-convert each step. the Thunderbolt-2 to Firewire cable is as rare as hens’ teeth though …
Can a Pi be hooked up to PCI-x? I think there are/were M.2 Firewire adapters as well.
(I might have some names wrong here, just going by memory)