Measures per line

Edit/Tools/Add/Remove.
See also: https://musescore.org/en/handbook/breaks-and-spacers

See https://musescore.org/en/handbook/tools#line-breaks

Note that breaks allow you to end a line after four bars if it otherwise would have gone on longer - just line line breaks in a word processor. But if you want to *increase* the numbers of bars on a given line, you'll need to make the staves smaller, or reduce the note spacing - again, just as you'd need to in a word processor. The staff size control is in Layout / Page Settings, and the global spacing setting in Style / General / Measure. You cam also override the global spacing via the "stretch" commands in the Layout menu.