I suspect (or hope) that Apple will release a new lightning to lightning cable with a upgraded DAC that support 24-bit high-res data. Such cable would make it possible to listen to the new high-res lossless music with the AirPod Max.
If not, you'll have to use the Apple lightning to USB adapter and then connect a third party DAC like the
DragonFly and then use the Apple
analog to digital cable to connect the DAC to the Airpod Max. If you'd like to use your MacBook or PC, you would need a regular USB cable to connect to a external DAC and then the 3.5 mm analog to digital lightning cable plugged in to the Airpods.
I've used my iPads and iPhones with the Apple USB adapter connected to my Hi-Fi setup DAC for years and played both streamed (Tidal) and localy stored high-res music (24-bit 96 kHz) without any problems. Both the lightning port and the usb-c port on current (and old) iPhones and iPads can pass on raw data to an external DAC to process without any bit loss.
My understanding of the AirPlay 2 transport is that it tops out at 24-bit / 48 kHz, but it would mean we can get lossless music wirelessly without any new hardware.
The headphones do not need support for a specific codec (ALAC, FLAC, ACC, MP3 or whatever) as the codec is handled by the DAC (either a usb attached one or a future one built in to the audio cable).