That's the problem with videos. They are easy to fake. I'm sure someone out there has a video for how to jailbreak and install Cydia on iOS 14.
Checkm8 is an tethered exploit. The device must be tethered before each boot. It's an exploit, but not a jailbreak itself. If anyone is running a untethered or semi-untethered jailbreak on iOS 13 right now it's either a private jailbreak or fake, no matter what they claim.