there is a bug called unable to open the project, check if it is made by gdevelop 5 properly or if you have authorization which is highly concerning, please fix the bug
Please give more context.
Where is saved the project?
In which folder?
Is the game.json file project is visible in the folder?
in documents, in the folder named gdevelop projects, yes game json file is visible
Is it possible for you to send us here or in private message the .json file to let us take a look at it.