The process for converting a TikTok video to an animated wallpaper varies, so it will be slightly different on an iPhone than it is on an Android phone.
Even better, you can turn the video in a live wallpaper if you just can't get enough of it. When you stumble across a video you like, you can download it onto your phone to watch over and over again. TikTok is great for creating short videos of people lip-syncing to songs or comedy sketches, but it's also very entertaining to just browse and share cool videos with friends.