You used to be able to chain three adapters:

Thunderbolt 3 to Thunderbolt 2 Thunderbolt 2 to FireWire 800 FireWire 800 to FireWire 400

to plug a modern Mac into an iMac G4 in Target Disk Mode

Now you need to add another layer: virtualizing old macOS on a modern Mac

But you can still use the original 2005 iMac G5 remote with a new Apple TV