Hello Andre,
I'm 100% sure what's causing this problem. It looks sort of like this... but I'm not sure.
It sounds like you may have already solved this problem, but here's what I think will work.
If you run conda info -e you can see all your conda environments. While your qiime-2019.7 environment might not have conda to update, your base environment will have a version of conda to update. So this should work:
conda update -n base -c defaults conda
Colin