can i charge my iPhone 12 max with an iPhone X charger?

Yes, but it won’t charge as fast as it will with a MagSafe charger or a 20W USB-C power source.

A nice feature of Apple’s world is that if the cable and plug fit it is safe to use it with any Apple device.

It will not be as fast of a charge than the newer 20 watt charger Apple sells.

yes