In short, we should just drink plain coffee, without milk and sugar ;)
More seriously, I am not surprised by those findings (in the sense that some unwanted effects have been found). I have never trusted these artificial sweeteners at all. I am however curious about the process yielding the observed impact in our gut microbe (as @bhoa) for the first study. This may be related to theit composition.
In short, we shouldn't drink anything at all.
Cos when you drink without milk and sugar, you might now have caffeine toxicity.
When I look at science, I just tell myself that prevent what is possible to prevent and work on other things.
I have not done so much study on sweetener but I intend to have a look at it
There is what health tells us, and there is what we like. Very often, those are not very compatible. I personally like coffee a lot, but as a plain coffee. I know exaggerating is definitely not good for my health... but I like it, so, I only try not to exaggerate ;)
For the rest, it is at the end a matter of that there is no free lunch. There is always a price to pay and we need to live with it.