You should be able to select the Kernel to use when you launch, and there’s a menu to change it up on the top-right:
That errors not one I’ve not seen. Looks like maybe your package cache got corrupted. You can delete package archives with conda clean -t. I would note that you can sometimes have issues mixing packages from the conda-forge channel and the main channel (mostly things with binary components not pure python). It also leads to that superseeded thing a lot. When you specify a channel on the command line it actually overrides the default channel. If you do conda install -c defaults -c conda-forge then it will keep main as higher priority which prevents some of the constant moving between channels.
I have recently been installing my environments solely from conda-forge with apparently good success (I did just have to reinstall one but I think I stuffed it up as I accidentally let pip pull in some core things). If you run conda config --help then you can see the commands to prepend channels and alter order (or just run conda config --show-sources and edit the config file). You can also have per-environment channel settings (conda config --env). So if you just add conda-forge before defaults before installing packages then you can get a whole enviropnment from conda-forge.