If it’s being charged by a non regular iPhone charger, this will happen. A lot of these videos are clickbait and misinformed videos. They are not 100% accurate.
They often use non-calibrated meters, confuse EMF noise from power transfer with dangerous radiation, or just plain fake the results.
The danger comes from cheap, poorly made chargers. These can cause overheating, short circuits, or even electric shock. That’s a hardware safety risk, not a radiation issue.
Using your iPhone while charging is safe. There isn’t any harm from radiation while you’re charging. However, it if displays an overheating message, then yes, unplug it and stop charging it.
But, it won’t catch fire or blow up on you. Charging your iPhone while using it is perfectly safe.