Removing the Playback Speed button

You can handle this only with JavaScript.

On the Slide Master, create a trigger to Execute JavaScript when the timeline starts:

var playbackSpeed = document.getElementById('playback-speed');
playbackSpeed.classList.add('hidden');		

This ensures the Playback Speed button is hidden on all slides, even if it's enabled in the Player properties.

Then, on each video slide, create another trigger to Execute JavaScript when the timeline starts:

var playbackSpeed = document.getElementById('playback-speed');
playbackSpeed.classList.remove('hidden');		

This will make the Playback Speed button visible only on video slides — or on any slide where this trigger is executed.