Different instruments for different voices using the same staff in MuseScore 4?

In MuseScore 3.X, I usually replaced the Choir Aahs with a string quartet when writing for mixed choir, because it sounded much more pleasant. That was quite easy to do because MS3 allowed for different voices in the same staff to be assigned different instruments in the mixer. This was very useful for condensed choral notation (SA|TB), as it allowed me to assign Violas to Tenors and Celli to Basses. I now wanted to test out the new choir sounds in MS4 but have as of yet not managed to assign the sounds to the appropriate registers using the mixer, because I can't seem to find a way to assign different instruments to different voices in the same staff.

Is the feature still around and I'm just technologically incompetent, or has it been removed in the switch from MS3 to 4?