Brightness, sound and text size bar not working in control center

1. Is this your corporate iPhone? Then please contact the system administrator of your corporate
2. If it is your personal device, in that case, do you have any profile installed by your corporate/organisation/enterprise/School Management?
   1. Erase the profile added by you If you have installed a profile on your own --> Install or remove configuration profiles on iPhone - Apple ...
   2. Or please contact the system administrator of the organisation who provided the profile to you

When a corporate profile (like a Mobile Device Management or MDM profile) is installed on an iPhone, it can control various parts of the device, including iCloud settings — but it depends on what the company has configured in that profile.