Maat Splitsen van 4/4 maat

You want to split the measure using a double barline?:
https://handbook.musescore.org/notation/rhythm-meter-and-measures/barli…

Or use two measures and adjust the Actual duration:
https://handbook.musescore.org/notation/rhythm-meter-and-measures/measu…

Right-click the first measure. (Don't right-click any note/rest; right-click on blank space within the measure.) From the context menu that appears, click Measure properties.... (It will be "Bar properties" in the British English version; obviously, I don't know exactly what it will be labeled in Dutch, but an equivalent.)

From the Measure properties dialog, change the Actual duration from "4/4" to "5/8" (yellow highlight). Click the Apply button at lower right (blue highlight), then click OK (green highlight).

Add the double bar line (yellow highlight) to the first measure and the Cut Time time signature (green highlight) to the second measure from their respective palettes. (Be aware that these palettes will not necessarily be in the order shown; I re-ordered them to shoe Barlines and Time signatures adjacent to one another! Also, your Time signatures palette will likely not show all the buttons mine does since I have created a number of them.)

Now, right-click the second measure and click Measure properties... again.

This time, change the Actual duration from "4/4" to "3/8". Click the Apply button at lower right, then click OK.

If you split the measure and then add the Cut Time to the second, it will re-adjust all following measures (including that one) to 2/2, which will not leave the 3/8 in that second measure. In that case, you'll have to adjust the Actual duration again for that measure.