Why is my Smart TV not recognizing any external devices?

Check the settings on your television to ensure that the input for the external device is enabled.
Check that all audio and video cables are correctly connected to the television and external device.
Check to see if any image size adjustments need to be made to view an image from the external device on the television.
Check the menu settings to ensure that the correct input selection is chosen.
Verify if the television is able to detect the connected device.
Perform a reset of the television by unplugging the power cable for 60 seconds.
Try connecting a different device to the television to see if it is recognized.