If you don't want a project to be visible in your account, you can stop it from being visible in the available projects list.
You can change a project’s visibility by changing the settings in Setup/Project/List My Projects.
The maximum number of projects that can be displayed in the Project Selector is 1000. If you have more than 1000 projects visible, consider hiding your inactive projects, so others can be accessed from the project selector. The List My Projects screen does not have this limit.
If you are working on a large number of projects, you can use any of the search fields at the top of the screen to filter the list. If the one you want doesn't appear when you press Search, it may be hidden. In this case you should select Hidden to show all hidden projects in the Search area of the screen.
If you don't want one or more projects to be visible to yourself / your account, you can hide them by selecting them in the list and then pressing Hide or Hide All.
If you've hidden one or more projects, but want to make them visible again, you have to select Hidden Show all projects that are hidden in the search area, then press Search.