Can I use the power adapter of Macbook Pro 2020 to charge for my iPhone 12 Pro Max?

The MacBook Pro, 13" 2000 model, is compatible with the 67W USB-C adapter, the 96W USB-C adapter or the 140W USB-C adapter.

The iPhone 12 Pro Max is compatible with the 20W USB-C Power Adapter, the MagSafe Duo Charger, the MagSafe Charger, or the MagSafe Battery Pack

Thanks caseyhb, I had no idea about this. The specs on the Apple store could do with a bit of extra information it would seem.

The 2020 MBP comes with the 61W charger which is one of those listed on the support page you linked.

Apple itself has tested fast charging the iPhone 12 via MacBook adapters: https://support.apple.com/en-us/HT208137

Correct - the two are not compatible. If it sounds wrong it probably is - "let your own discretion be your tutor".