20W charger to charge macbook

You can charge your 13-inch MacBook Pro with the 20W USB-C adapter for iPhone and iPad. It will charge your Mac much more slowly than the included 61W adapter, and if you're using your device while it charges, you might notice that the battery will slowly drain. If you leave your Mac charging overnight while you don't use it, it won't damage the battery in your Mac, but it will charge significantly more slowly.

Find the right power adapter and cable for your Mac notebook - Apple Support

"You can use a compatible higher wattage power adapter without issue, but

it won't make your computer charge faster or operate differently. If

you use a power adapter that is lower in wattage than the adapter that

came with your Mac, it won't provide enough power to your computer."

I doubt a 20W power adapter for an iPhone or iPad will do anything for a MacBook Pro.

MacBook Pro uses USB Power Delivery Protocol. The device and Smart Charger negotiate the voltage level and Amperage for charging, typically 20 Volts level and many more Amps that an iPhone changer can provide.

iPhone and iPad chargers generally use default 5 Volt charging. Such a charger can not "force itself" on your MacBook Pro -- the MacBook Pro controls charging at every turn. The MacBook Pro will likely see such a device as incompatible, and ignore it.

The MacBook Pro is an expensive piece of gear. You should use the correct charger to power it. Using a "too small" wrong power adapter could turn it to junk.