There is no button can hide a project. But as a Project Collection Administrator (PCA) or Organization owner, you can set a specific project to be visible or invisible to someone.
You must have a private project.
Go to Organization Settings >> Users >> select the user and click "manage user" option.
Disable the project which you don’t want this user to see.
----------
Please don’t forget to "Accept the answer" and “up-vote” wherever the information provided helps you, this can be beneficial to other community members.