Help for Project-Structure

For some time ago i start with a complex Project in VS2019. This project has some Classes that are used generell (i named then ‘Framework’). The huge of other classes are the application. The framework and Application will modified from time to time.

Now I will create a new Application. How can I structure them, that following can do:

  1. Framework and Application in the same VS2019-Projectfile, so that i can directly modified the Framework-Classes if it needed.
  2. No duplicate Files of Framework-Classes (Prior-Application and New-Application)