The "Répertoire d'installation" is the folder where your realMyst game is installed. But I see that your don't have the original "realMyst" but the "Real Myst Masterpiece Edition", which is a different game.
Well, I don't remember if the patch is compatible with the Masterpiece version, so, you will have to try, but save your Masterpiece folder somewhere else before installing the patch.
"Myst" isn't "realMyst", so, the patch will not work with "Myst".
Would you have knowledge in Python so that I could make the digicode that I had already told you about. Or, do you know someone who can help me or a forum?
I don't know enough Python, sorry. But anyway, you'd have to know if Blender UPBGE is compatible with Uru, before to continu working with Blender UPBGE.
For tutorials to help you to build your Age, take a look here: https://guildofwriters.org/wiki/Tutorials#Korman (the tutorials for Korman ends at "Korman:Relto Pages: create your own Relto page.")