Sometimes Big Sur updates seem to unset Screenwriter 6.7's security permissions. The crash report often starts with this:
A Critical Error Has Occurred
Assert: inFontName.IsNotEmpty() Failed
The first thing to try is to reset the permissions.
Occasionally, resetting those permissions does not seem to fix the problem. When that is the case, we recommend reinstalling the most current version of the program, even if you have the most current version. Here is a link to reinstall:
After reinstalling, we recommend that you remove and re-add Full DISK ACCESS per the "Giving Screenwriter 6.7 Permissions..." link above.