What audio formats can the iPhone 12 Pro Max playback?

Audio Playback

• Audio formats supported: AAC‑LC, HE‑AAC, HE‑AAC v2, Protected AAC, MP3, Linear PCM, Apple Lossless, FLAC, Dolby Digital (AC‑3), Dolby Digital Plus (E‑AC‑3), Dolby Atmos, and Audible (formats 2, 3, 4, Audible Enhanced Audio, AAX, and AAX+)
• Spatial audio playback
• User‑configurable maximum volume limit

iPhone 12 Pro and 12 Pro Max - Technical Specifications - Apple

ok. I think 24/48 is the best you'll do. My app (roon) downsamples from 24/96 to 24/48 playing on the device - so I believe that's the dac limit. If you use an external dac like described in the article, you'll be able to go higher. Apple Music may downsample without telling you so it may appear to work. Honestly, be careful of those high res files... I used a spectrum analyzer on mine and many were no different than the "lesser" quality... they looked upsampled. I keep high res and downsampled versions in my Roon library and only downsampled in my Apple Music and Plex libraries. Good luck. I hope I gave you a few insights that help you.

As Johnathan Burger pointed out, Apple Lossless Audio Codec is ALAC. If you understand the differences between AIFF and ALAC, then the simple answer is yes, it plays both formats. If you don't understand, then both formats are "high quality", but AIFF is not compressed, whereas ALAC is compressed. But unlike mp3, aac, or similar lossless compression, ALAC and FLAC are lossless, meaning no data is lost during compression. If you're not an audiophile and you want to maintain lossless quality, recommend going to ALAC. You'll save a bunch of disk space. Go to AAC if you're ok with lossy and want to save a lot of space. If you are an audiophile you'll pick whichever format you prefer at the expense of space... so have at it. Good luck.

It's a complicated topic due to the choices in the workflow you use to listen to music. Variables include hardware (phone and headset), software, and protocol limitations (e.g., Bluetooth). If you use Apple Music with iPhone and Bluetooth headset, stick with max 16bit / 48kHz (some say 24bit) for your encodings. Don't upsample...ever. 96->48 or 88.2->44.1 or 32->16 or 24->16 is ok. If you go all audiophile, the only real way is to not use Apple Music at all. You can be a tweener, and that's when it gets complicated. Here's a link with more info to get you going: https://www.whathifi.com/advice/how-to-play-hi-res-music-your-iphone-0

Apple lossless is listed right there in the specs.

That is what Alac is.

Apple doesn’t give out specifics.

What I posted is all Apple says.