https://wccftech.com/64gb-ram-option-is-only-available-on-macbook-pro-with-m1-max-chip/

Before you configure your MacBook Pro to 64GB of RAM, you should know one important detail about that particular upgrade.

See, the thing is, you can upgrade to 64GB of RAM on the new 14-inch and 16-inch MacBook Pro laptops. But, before you do that, you have to upgrade to the M1 Max chip as well. That's right, if you are buying an M1 Pro notebook, you can configure it up to 32GB of RAM only.