When I go to File > Finalize Project to save a clip, nothing happens. No light gray bar, no "in progress" messaging or symbols, no output.
How do I export/save a clip so I can view it outside iMovie?
You can use the SHARE menu. Use SHARE/EXPORT MOVIE in the size you need. Or use SHARE/EXPORT USING QUICKTIME if you want to control the export parameters.
Finalize Project will create a Media Browser copy for all available sizes. If you have already finalized, it will not do anything unless you do further edits. In this case, your Media Browser copies are deleted and you can Finalize or Share again.