Charge iPhone12 with a non-MagSafe wireless ?

You can use any QI certified charger.

It will take twice as long to charge. Fine if you want to leave it overnight.

So, assuming if it is the same "style" that it is Qi and will work.

I hope so, we've got 3 scattered around the house and I do need a new 'phone :-)

I assume a Belkin BOOST, bought from Apple Store this May is a Qi device? How can I find out? And I'm also reading that some Qi devices don't work?

That is the same style that Apple now uses.