The command should be conda activate mfix-23.1.1 (or mamba activate mfix-23.1.1 if you are using Mamba)
Please upgrade to 23.2 when possible
The error you posted looks like what happens when you are running MFiX remotely. In this case you may need to install VirtualGL and use the command vglrun mfix
Error is coming when create the Mfix environment in conda:
UnavailableInvalidChannel: HTTP 404 NOT FOUND for channel new_channel_url https://conda.anaconda.org/new_channel_url
The channel is not accessible or is invalid.
You will need to adjust your conda configuration to proceed.
Use conda config --show channels to view your configuration’s current state,
and use conda config --show-sources to view config file locations.