Apple's Thunderbolt FireWire 800 adapter daisy-chained with their TB2-to-TB3 adapter should work on any modern system with Thunderbolt and FireWire support, as it just presents as a bog-standard PCI FireWire card.

So worst-case, you should be able to access your old drives on a modern Mac by booting from a FireWire-compatible OS (Asahi or older macOS) on an external drive.