Playback of individual parts of a score

While you can play only specific measures, I don’t believe that you can export only specific measures. The Playback controls have no effect on exporting.

The two instances of the word “optional” in handbook.musescore.org/sound-and-playback/playback-controls#play refer to specific things that are possible.

If you simply click the Play button (or press Space), it begins playing the score from either the beginning or from the last-selected note. Optionally, you may click a single note to make it be the starting point.

If you select a measure in a single stave and click the Play button, only that staff will play. Optionally, you may select a “range of staves” by Shift+clicking in a different staff. This selects a measure (or several) in multiple staves. At that point, clicking the Play button will play only the selected staves.