Done, I already added the video to the gallery section. If you want to add a video to the gallery section of a page by yourself, simply add the YouTube video you want to add in the gallery page: https://gta-myths.fandom.com/wiki/Special:NewFiles

Click on "Add Video" which is located in the top right, and simply put the video URL in the user input. After that, refresh the page (if the video didn't appear in the list) and copy the video title. Now, go to the page where you want to add the video, scroll to the gallery section and edit its template. In the "Search for media" search box, paste the video title that you just copied, and finally, click apply.