Fitness app not available on iPhone 13 pro max

Hello aurelien2a.

Thank you for using Apple Support Communities. You mentioned that you're unable to install the Fitness app. If so, allow us to share some information with you. There are certain requirements needed in order to be able to use the Fitness app. Check out this link below:

How to get Apple Fitness+ - Apple Support

Under "Here's what you need", it states the following information: "Make sure that you have an Apple Watch Series 3 or later and an iPhone, iPad, or Apple TV that's compatible with Apple Fitness+."

If you don't a compatible Apple Watch paired to your iPhone, you won't be able to use the app. Additionally, you want to make sure you're in a region that supports this feature: Availability of Apple Media Services - Apple Support

If you're using the correct devices and you're in a supported region, yet you're unable to instal the app, try restarting your devices:

Restart your Apple Watch - Apple Support

Restart your iPhone - Apple Support

We hope this information is helpful. Cheers.