Sometimes it makes sense to have just few bars of music and a multirest in a line (in a part). Is there a way to stretch the multirest, so that it fills a wider part of the line?
This is how it looks now. The music is too wide, as the multirest is too small.

One way to do this is with note spacing changes.
Select the multi bar rest and add a note spacing change (Engrave > Note Spacing Change) that resets the default quarter note spacing.
Then select the first note of the system and add a note spacing change that changes this value to something smaller than the current value. This will condense the first two bars, and the multi bar rest will get bigger to compensate.
(You may also need to include Minimum space for short notes in your change and reset.)