Late but I wanna give a hindsight for future developers.
Every computer has something called HWID, your Motherboard and CPU have it. Now, everytime someone downloads the game, it can auto generate a key. This key will be associated with the HWID and there are two ways of doing this.
LOCAL
Your game gets associated with the PC and only will open if played on that exactly PC.
Problem:
There are ways to emulate the HWID.
ONLINE:
You set server where each copy will register the HWID associated with game copy or even better, you create an AUTH, like two-factor accounts, where your game has one key and the server the other token and when you try to play the game it connects to that server and verifies if you are the legal owner.
Problem:
Price, at least 20 dlls per month if you try to set a MySQL server on AWS.
In both scenarios it can still be cracked but at least it wont be a kiddo who copy and paste the .RAR file on facebook or put the MEGA link on a discord server.
Plus, if they want to risk their computers to get bricked and very very probably not even get the last version of your game instead paying 5 to 10 US dlls is up to them, don’t you think? 