Ecrire une mesure

I am in the situation where a note of a certain value, for example a dotted half note ("blanche pointée" in French) the coexists with quarter notes ("noires"), as in the upper score. (see the attached file).

The solution I have adopted in Musescore (It is crazy ! ) is to transform the dotted half note into three quarters of the same height.

Thank you by advance to tell me how to respect the score?

H. Mensch