It is still not clear to me how legal documents on document sharing platforms are legally enforceable when signed by clicking buttons.

https://www.upcounsel.com/three-key-elements-of-a-binding-co... explains the basics. At its heart:

1. There must be an offer.

2. There must be evidence that it was accepted.

3. There must be consideration - each side potentially gets something of value to them.

If all of those elements exist, it is a legally binding contract under Common Law. (Unless, of course, some law says that it isn't. For example you can't be held to a contract to break the law, and verbal contracts are often not binding in real estate.)

I am not a lawyer, this is not legal advice.