Converting null literal or possible null value to non-nullable type.

Possible null reference assignment.

Cannot convert null literal to non-nullable reference type.

Cannot convert null literal to non-nullable reference type.

The variable 'e' is declared but never used

Dereference of a possibly null reference.

Non-nullable field 'audioDeviceComboBox' must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring the field as nullable.

Nullability of reference types in type of parameter 'sender' of 'void AudioOutputForm.audioDeviceComboBox_DropDown(object sender, EventArgs e)' doesn't match the target delegate 'EventHandler' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'sender' of 'void AudioOutputForm.audioDeviceComboBox_SelectedIndexChanged(object sender, EventArgs e)' doesn't match the target delegate 'EventHandler' (possibly because of nullability attributes).