Thanks for the information. Now to see if I can duplicate what's going on and fix it.
On what system did you play the game when you made the video? I notice that the game background doesn't clear as it should. (The title background shouldn't be visible at the top at all while playing the game.)
I answered on Steam, but will post this here, too:
Usually the key is a link. However, if it's just the key (a bunch of random letters) try adding this to the beginning: https://fascimania.itch.io/kilgazar/download/ If that doesn't work, contact me at email@example.com and I'll help you out. Please let me know either way.
I believe they are found on your my purchases page. You might have to click the "download" button in order to open up the game information. None of my purchases here have keys, so I don't know this for certain.
If the purchase was part of Groupees Build a Greenlight Bundle 44, the key will be found on that site not this one. If you got an itch.io key for the game via trade, ask the person to give you their Steam key as well.