To stop the DVD player application from launching when a DVD is inserted, follow the steps below:
1. Click the Apple menu and then select "System Preferences" from the drop-down list.
2. Now, select "CDs & DVDs".
3. Click the drop-down menu next to where it says "When you insert a video DVD", and then select "Ignore" from the list.
4. Close System Preferences.
If you just want to stop the DVD player application from going into fullscreen mode, ignore the instructions above and follow these steps:
1. Open the DVD player app.
2. From the menu bar, select DVD Player → Preferences.
3. Click on the "Player" tab and deselect "Enter fullscreen mode".
4. Click the "OK" button to confirm.