What is the procedure for software licensing when purchasing keys (in particular, Windows)?

Question

Licenses for software and other works

After a long discussion in the comments to https://qna.habr.com/q/1089912
, some doubts arose.
I understand that everything happens like this:
1. A person purchases a box
2. During installation, he accepts the license agreement and the attachment agreement (what does it look like by the way?)
3. After entering the product key, its copy becomes licensed.
It is correct?

And an additional question about the keys from ebay / ali for 100r - is it still legal, or not? Why?

And another question: The term "licensed device" has arisen, and some interpret this as the fact that a person does not have a license in principle. And if the publisher sends updates to this device, then the copy is recognized as licensed.
If so, how can you prove it in a piracy trial?
Or is the exploitation of such software features considered a circumvention of the license agreement => is it piracy?