Premiere Pro stalls when opening project

Yes. I was forced to install 2021 v15.1 (ugh) for a project I inherited from a client.
Currently running Mojave OS as I'm still afraid of what won't work with Catalina etc.

PP2021 worked flawlessly for about half a day, then crashed.
Since that crash, every time I open PP2021 and attempt to open a file it has previously opened, it hangs and beachballs as you describe. Happening on multple projects files with nothing in common bar the software.

I found a workaround WHICH I SHOULDN'T HAVE TO WASTE MY TIME DOING ON A PAID PIECE OF "PROIFESSIONAL" SOFTWARE...

If you open PP2021 and create a new project it will open fine, then you can use File->Open project to open the project file that moments ago would not open... Like magic.

I now have about 30 blank project files on my desktop, since working with this project.

Thanks again Adobe, top job as always. 

Moved to the Premiere Pro forum.

Try resetting the preferences:
https://community.adobe.com/t5/Premiere-Pro/FAQ-How-to-reset-trash-preferences-in-Premiere-Pro/td-p/8236158

If that doesn't work, try resetting the Workspaces:
Reset a workspace
Reset the current workspace to return to its original, saved layout of panels.
1. Do one of the following:
• Click the Workspace menu icon and select Reset to Saved Layout.
• Choose Window > Workspace > Reset to Saved Layout.
from here:
https://helpx.adobe.com/premiere-pro/using/workspaces.html

If that doesn’t work, try updating or rolling back your graphics driver directly from the video card manufacturer’s site.

Also, please help us help you:

https://community.adobe.com/t5/premiere-pro/faq-what-information-should-i-provide-when-asking-a-question-on-this-forum/td-p/3929027?page=1