I would like to know if it is possible to know how many people have used the code that I for example post on twitter. I would like to know the exact number of people.
Also I have a second question, is it possible to create a special link to the mode, and understand how many people clicked on this link?
Yes I want to give the youtuber a link to the game (or create a unique link), and after publishing the video to check how many people clicked on the link thus finding out the audience reach and how many people came to me from it
In that case, like what @lV0rd said - no, there is no official Roblox way to generate links that can count the number of clicks.
You’ll have to use analytics under your game to see if there was a spike or massive change in the amount of Players in your game, when this specific YouTuber made a video about your game.