I’ve been experimenting a bit with the melody blocks in MakeCode for the micro:bit and I can’t get them to play more than one note at the same time. I ended up going with a monophonic melody. It’s interesting that the V2-only sound effects can play at the same time as the melody, you can hear the two together in this YouTube video from the small V2 speaker.
The sound effects appear to play sequentially even if you try and play two in the background. Same question on polyphony there.
And I’d like to be able to lower the volume and possibly silence the melody but leave it playing and be able to then play sound effects and later unmute the still playing melody. I can’t work out a way to do that.