Why do shaders compile indefinitely, when I open up 4.21?

I have recently gone to upgrade to 4.21, and after several attempts have had to continue using an older engine version.Whenever I start a new project, or attempt to update an existing project to the latest version, Shaders begin to compile indefinitely. I have left my computer on for up to 2 hours+ with no shift in the amount that is being compiled. Any help or advice on this would be great!