I just found a workaround for this.
I have some “cues” which I only want the conductor to see, but they are “glued” to the uppermost part in the score, which means that in this case they also pop up in the “Flute 1” part, which I don’t want.
When in the part, select the text you want to hide, press the “Color” switch in the bottom panel, and then press the small black square that pops up to the right of the “Color” text. Then, drag the Opacity slider down to 0%. Voila, the text is gone (or rather invisible), but only from the part. It is still visible in the score (or vice versa).