Don’t “quit without saving” - you will definitely lose your work. The following may work. Since you can’t save your project you have nothing to lose. I’ve never encountered this problem so I don’t know for sure that this will work.
Do Apple (menu) > Force Quit then choose Audacity. The unsaved project should still be available in the Audacity temp directory and you should see a project recovery dialog next time you launch Audacity.
Reset the Audacity preferences following these instructions: https://forum.audacityteam.org/t/resetting-audacity/50613/1
Although it really shouldn’t make any difference, you could also download and re-install the latest Audacity version from here.
Now start Audacity. You should see the project recovery dialog. If you project is recovered, try saving the project.
– Bill