AutoCAD Architecture 2024 toolset creates a backup APJ file that you can use to restore your APJ file in the event of the original file getting corrupted or accidentally deleted. The backup file is in the same folder as the original APJ file and the file extension is .ap$, for example <projectname>.ap$. Change the extension of the <filename>.ap$ to <projectname>.apj to restore your APJ file.
When a project's APJ file is deleted or corrupted, the project will not display in the Project Browser anymore. The DWG files and XML files contained in the project are not impacted and are still available.