@AliFarahat published a presence plugin “Efactive”, described here:
I’ve not played around with it, so don’t know exactly how it is that it works, but perhaps it’s a decent solution for detecting user presence in Bubble.
(BTW, this general concept is called “presence”. A quick Google for “how to add presence to a web app” turned up this nice overview from Firebase. This would be another potential solution that could with a bit of work be implemented in a Bubble app: