You found a 100w USB-C charger? I think those are kinda rare?
It would help if you posted specifics about it. I believe the most the 12 Pro Max will take is 20W, but you need a very specific USB-PD profile (2.22A x 9V), otherwise you're looking at the more common 18W via 2A x 9V. Again, depending on if this mystery charger supports such a profile.
When in doubt, just use one of your "old" iPhone chargers 🙂