Can I use an older charging adapter for my new iPhone 14 Pro Max?

You can use the power adapter and cable from previous phones. See the following from Buy iPhone 14 Pro and iPhone 14 Pro Max - Apple

We encourage you to re‑use your current USB‑A to Lightning cables, power adapters, and headphones, which are compatible with these iPhone models. But if you need any new Apple power adapters or headphones, they are available for purchase.

You’re referring to the newer USB-C power adaptors.

Fundamentally they are not “different” from the older USB-A adaptors … it’s a DC power source …

… However they ARE more complex AND they DO come in a wide range of outputs to supply many devices and negotiate the variable DC-voltage power-delivery protocol with the powered device.

A 20w USB-C adapter can charge ANY iPhone at up to the phone’s “maximum charge acceptance rate.”

False.

See what Apple says in my previous post.

FWIW, I’ve been charging my own 14 w/ an OLD 5w icecube power adaptor every night.

As long as the phone is receiving properly-regulated DC voltage it’s “happy.”

Indeed they can.

I’m “overnight charging” Apple’s latest “Flagship” iPhone w/ a USB-A “Ice Cube” originally supplied w/ an iPhone 5s.

Absolutely safe.

Not “fast” but def safe.