Hello clozner,
Welcome to Apple Support Communities.
We understand that you’re concerned about the same downloaded music files showing as a different size on iPhone and Mac. We are happy to help.
Since lossless audio is a high quality, then you should not experience any difference in the music quality for the music downloaded to your Mac or iPhone. Here’s how to determine what you need to listen to lossless music: About lossless audio in Apple Music - Apple Support
"How to listen to lossless on your iPhone or iPad
What you need
You can listen to lossless on an iPhone or iPad updated to the latest version of iOS or iPadOS using:
- A wired connection to headphones, receivers, or powered speakers
- The built-in speakers
- To listen to songs at sample rates higher than 48 kHz, you need an external digital-to-analog converter.
How to turn lossless on or off
- Go to Settings > Music.
- Tap Audio Quality.
- Tap Lossless Audio to turn it on or off. From here, you can choose the audio quality for streaming and downloading audio.
- Lossless for a maximum resolution of 24-bit/48 kHz
- Hi-Res Lossless for a maximum resolution of 24-bit/192 kHz
How to listen to lossless on your Mac
What you need
You can listen to lossless on a Mac updated to the latest version of macOS using:
- A wired connection to headphones, receivers, or powered speakers
- The built-in speakers
- 14-inch MacBook Pro and 16-inch MacBook Pro support native playback of songs at sample rates up to 96 kHz.
- To listen to songs at sample rates higher than 48 kHz on other Mac computers, you need an external digital-to-analog converter.
How to turn lossless on or off
- Open the Apple Music app.
- In the menu bar, choose Music > Preferences.
- Click the Playback tab.
- Under Audio Quality, select or unselect "Lossless audio" to turn it on or off. From here, you can also change the settings for streaming and downloading lossless.
- Lossless for a maximum resolution of 24-bit/48 kHz
- Hi-Res Lossless for a maximum resolution of 24-bit/192 kHz"
Let us know if you have further questions.
Take care.