If you have two or more monitors and you want your videos to open on a second or third monitor, full screen, then do the following:
Go to Tools and then Preferences or press Ctrl + P. Click on the Video icon towards the top.
Check on the Fullscreen option in the Display section.
Then next to the Fullscreen Video Device option. It’s probably set to Automatic. If I wanted VLC to automatically play on my second monitor, I would click on the word Automatic and switch it to \\.DISPLAY2
If you have more than two monitors, you’ll probably see them all listed there. Choose accordingly.
Then click on Save. Now when I double-click on a video to play it, it opens full screen on my second monitor. If your settings don’t seem to be holding, change your settings and then shut down and restart VLC.