screen sharing

In addition to Tessarax’ recommendations, with which I agree:

ridhasait7 wrote:

Actually my brother has done it & he’s invading my privacy

Be certain you are the only person using your Apple ID. Change that password at a minimum.

Change your Apple ID password - Apple Support

Ok, give the following a try:

To disable screen sharing on an iPhone:

1. Open the Control Center on your iPhone by swiping down from the top-right corner on devices with Face ID or swiping up from the bottom of the screen on devices with a Home button.
2. Tap the "Screen Mirroring" icon. If you don't see this icon, swipe left or right to find it.
3. If it is highlighted, then it is enabled. Just tap on it so that it is not.
4. Screen sharing should now be disabled.

Note: You can also disable screen sharing using the AirPlay feature in apps that support it. Simply tap the AirPlay icon in the app and select the device you want to share your screen with.

If neither of these works, then you will need to restore your phone to bring it back to it "out-of-the-box" configuration. This will completely erase your phone and any data on it will be lost. You will then need to restore that data from a backup that you have been making to either iCloud or to your computer.

Tap on Settings > Control Center, then check to see if "Screen Recording" has been enabled. This is what would allow your phone to share its screen to other devices.

Otherwise, someone would have to have physical access to your phone to install a screen sharing app.

See this page from the iPhone User Guide.

Share your screen in a FaceTime call on iPhone - Apple Support

Ok, then why don't you just ask them what it is and have them show you how to uninstall it?

Alternately, you can find out the list of apps installed on this phone by going to Settings > General