The new scene is missing an Event System component. This is what sends the events to the buttons.
Unity doesn't issue warnings for missing EventSystem components because it's designed to be flexible. Some scenes might intentionally omit an EventSystem (e.g., custom solutions, scenes without UI interaction, or shared EventSystem setups across multiple scenes). Adding a warning would risk false positives and disrupt workflows. There is also no good place to do a check for the EventSystem. Interactive elements are not aware of the EventSystem and should not be checking for it. This would come under a feature request.