Since I'm personally most interested in practicing to draw humans (exactly because they are difficult and I suck at it) there'll be always prompts for that. In the first posts I mostly offered two exercises for drawing humans and three with other stuff, though if I go down to three prompts it'll likely be one for humans and two other stuff that sometimes maybe could be done with humans or not depending on what motif you choose.
I get what you're saying about exercises that are not too involved, I'll keep that in mind, but I admit that I don't quite understand how your examples are much simpler. I mean, I actually offered some of those examples? Like "object under different types of lighting" was the fourth prompt of week 3? "portray different moods" was more or less all that the emotions and the body language prompts of the first two weeks asked for... so to me it seems the prompts I chose are about as complex as your examples? I mean, I find drawing animals in motion really hard for example, since you have much less opportunity to watch and study how they work whereas you observe humans daily and can make a movement yourself as long as it is nothing extravagant, so any (good) animal action drawing would be a project for me that requires searching for reference, possibly even video to see how an animal looks like.
I admit that I have no interest in doing abstract art myself (though I love looking at it), so I find it really hard to come up with potential exercises for that, unless someone would appropriate rather general composition prompts like the one for spotting blacks from last week for abstract art (I mean, the prompt just said "Draw an image with an interesting pattern of black areas and shadows" you could do that without drawing objets). But I'm more than happy to include prompts suggested by others, so if you have good ideas for abstract one, I'd love to hear them.