About screenshot

If you can't do that after reading the support article I posted, try a "forced" restart of your iPhone:--> Force restart

iPhone – Apple Support

If the issue still persists, I suggest that you make an appointment (*) and have your device inspected at an Apple Store or AASP (Apple Authorized Service Provider) among this list:--> Apple – Location Selector. After checking it out, they'll give you all the available options.

Regards

Giulio

(*) You can do it:

Online:--> Genius Bar Reservation and Apple Support Options - Apple;

Contacting a local Apple Store or AASP among the list provided above;

Using the "Apple Store" app, available and downloadable from AppStore.

See these instructions:--> Take a screenshot on your iPhone - Apple Support

Regards

Giulio

sreenu ~ Apple's iPhone User Guide says: "If your iPhone isn’t working as expected, you can try restarting it by turning it off, then turning it back on.":

Turn iPhone on or off - Apple Support

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