measures per line

Add a system break every 4 measures.

See https://musescore.org/en/handbook/4/systems-and-horizontal-spacing

You can manually use a system break every 4 measures: select every 4th measure and simply press the Return key.

In MuS 3 there is also a function Format -> Add/Remove System Breaks, where you can specify a number "Break systems every x measures". I don't know anything about MuS 4.

But this only works if your notes don't need more space than can fit in 4 measures per staff.