MuseScore creates these automatically when you generate parts from your score using File / Parts. However, if for some reason you are entering a single part only and not the full score, you can convert regular rests to multimeasure rests using Style / General / Create multimeasure rests (or shortcut "M"), once you have finished entering your notes.
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MuseScore creates these automatically when you generate parts from your score using File / Parts. However, if for some reason you are entering a single part only and not the full score, you can convert regular rests to multimeasure rests using Style / General / Create multimeasure rests (or shortcut "M"), once you have finished entering your notes.