Trying to set an "in-Out" range of the movie to share it causes crash

Start by deleting the application preferences. Do so every time the application crashes, or behaves unexpectedly.

To delete preferences, hold down command and option while starting FCP X and click Delete Preferences.

Reopen your library and try again.

Often that is all it takes.

If that is not enough, drag the application to the trash (don't empty it yet), and download a fresh copy from the App Store.

If the problem persists, tell us more. Run Etrecheck and post its full report here.

Note that if you delete the preferences, FCP X will revert to its original default layout with no Library etc. opened.

You will have to navigate to the Library you were working with and open it.

Any special settings you have made in the app will also be lost.

To avoid losing special settings in future, you can use a free app called Preference Manager that was developed by a contributor to this forum.

https://www.digitalrebellion.com/prefman/

When you have FCP X up and working well, you can save the preferences to Preference Manager and then, should you ever need to delete them, you have a good working set you can install.