There isn't a signal because PathFollow3D doesn't do anything on its own to move a Node. It just finds a point on the parent Path3D based on it's progress/progress_ratio value.

I would suggest wherever you are updating the PathFollow3D's progress, add a check for:

if path_follow.progress_ratio >= 1.0:
    # do something here, like emit a custom signal

I know some people with privacy concerns will go out of their way to avoid any "smart" devices that communicate over WiFi. If you stick with Z-Wave/ZigBee/Matter, you don't have to worry about any sort of external communications. I mean, even with WiFi devices you can isolate them by making a separate local-only network, but that's a pain.

Hope they pull through. Cohost is the most fun I've had on social media ever