No 'sync music' check box to check

With Apple Music you do not have Sync Music in stead you have

Turn on Sync Library with Apple Music

If you subscribe to Apple Music, you can turn on Sync Library to access your music library and music that you've downloaded from Apple Music on all of your devices.

Here's what you need

• Update your iPhone or iPod touch to the latest version of iOS, iPad to the latest version of iPadOS, or Mac to the latest version of macOS. On a PC, make sure that you have the latest version of iTunes for Windows.
• Subscribe to Apple Music or iTunes Match.
• Sign in to all of your devices with the same Apple ID that you use with Apple Music or iTunes Match.
• Connect your devices to the Internet over a Wi-Fi or cellular network. On a Mac or PC, you can also connect to the Internet using Ethernet.

Apple Music availability varies by country and region. Learn what's available in your country or region.

Turn on Sync Library

Turn on Sync Library

With the latest version of iOS, iPadOS, and macOS, Sync Library is turned on by default. If you turned off Sync Library, you can turn it back on. Just follow the steps below for your device.

On your iPhone, iPad, or iPod touch

1. Go to Settings > Music.
2. Turn on Sync Library. If you don't subscribe to Apple Music or iTunes Match, you won’t see an option to turn on Sync Library.

If Sync Library is updating or turned off, you'll see a message at the top of the Library tab in the Apple Music app.