Welcome to the forum!
Enforcing a single login at a time isn’t something you can do by changing a setting. You would need to code it into your app. The only approach I can think of is to generate a random id (e.g. a UUID4) when a user logs in, and store it in both the Users table and the server side session.
At some point in the login process (after the user logs in, but before you generate the number) you can check to make sure the session and User table values match. If they don’t, you can do whatever you want. In your case generate a new random value.
In every server side function that is used by logged in users, you can check the two values to see if they match. If they don’t, return an error that the client code can use to log the user out.
Hopefully someone else will come up with a simpler approach.