This is vastly more difficult than you think. For example, if you try to use the standard method, which is hard drive serial numbers, it's incredibly easy to spoof AND all prebuilt computers from Walmart share the same serials. Non-starter.
https://stackoverflow.com/questions/47603786/where-do-window...
Because I help develop a game engine / platform that deals with this problem and therefore done extensive research?
All of those Microsoft device ID variants are trivial to spoof or collide. If you're talking about GetSystemIdForPublisher() and friends like 'Product ID', you get the Walmart collision problems.
https://github.com/topics/hwid-changer
Furthermore, if you rely on an easy-to-spoof hardware ID system, if someone gets ahold of someone else's HWID (see: database breach, phishing), you can trivially mess with the data.
Valve/Microsoft/Epic get around this by spending tons of developer time on this problem and using techniques like fingerprinting and behavior analysis.
> if you pair it with some kind of online login system
Unity does not have that and there is no way in hell that they will be able to force all players of all games made in unity to sign up for one.