System services iOS 14.4

This has nothing to do with it. I have several Apple devices, iPhone, iPad, Apple Watch, and MacBook Air, all signed into the same Apple ID. I'm also the Family Organizer of our Family Sharing setup. If you go to Settings>Privacy>Location Services>System Services, you can see Device Management, and you can turn that off there. I'm not sure of the real function of that setting, but it does not have to do with having multiple devices on the same Apple ID.

See this support page-> Intro to mobile device management (MDM) - Apple Support

Regards

Giulio

Company iPhone or owned by a school?

Where, exactly, did you buy it?

Open "Settings" App. Scroll down and then tap on "General" section from the left menu. Scroll down all the way and then tap on "Device Management" Then tap on "MDM Profile"