Libmamba broken on MacOS M1

Something seems to have happened since mamba got installed. I did an update of my conda installation, and when installing some packages through conda-forge, it saw:

 - conda-forge
 - defaults
Platform: osx-arm64
Collecting package metadata (repodata.json): done
Solving environment: \ warning  libmamba Added empty dependency for problem type SOLVER_RULE_UPDATE

Now, not only do the packages I wanted to install not work, but my installation seems utterly broken. For instance:

(base) grs53@:~$ conda update --all
Error while loading conda entry point: conda-libmamba-solver (dlopen(/Users/grs53/miniconda3/lib/python3.11/site-packages/libmambapy/, 0x0002): Library not loaded: @rpath/libarchive.19.dylib
  Referenced from: <027768CD-20C9-3E75-850D-35E842A32FA5> /Users/grs53/miniconda3/lib/libmamba.2.0.0.dylib
  Reason: tried: '/Users/grs53/miniconda3/lib/libarchive.19.dylib' (no such file), '/Users/grs53/miniconda3/lib/python3.11/site-packages/libmambapy/../../../libarchive.19.dylib' (no such file), '/Users/grs53/miniconda3/lib/python3.11/site-packages/libmambapy/../../../libarchive.19.dylib' (no such file), '/Users/grs53/miniconda3/bin/../lib/libarchive.19.dylib' (no such file), '/Users/grs53/miniconda3/bin/../lib/libarchive.19.dylib' (no such file), '/Users/grs53/miniconda3/lib/libarchive.19.dylib' (no such file))

CondaValueError: You have chosen a non-default solver backend (libmamba) but it was not recognized. Choose one of: classic

Any help would be appreciated.

Fixed this with:

conda install conda-forge::libmamba  

New users who want Mamba as a frontend shouldn’t start from Anaconda or Miniconda. Instead, they should start from Miniforge.

Conda Forge is currently the only source for Mamba and it is not recommended to ever mix defaults and conda-forge packages in the same environment. Miniforge comes with Mamba and sources from Conda Forge by default.

If replacing the base install is not possible (e.g., it’s been around for a while), then the alternative is to update all packages with conda-forge prioritized:

conda update --all --override-channels -c conda-forge -n base
conda config --add channels conda-forge

That should be done prior to installing Mamba.

See also Latest miniconda incompatible with mamba? · Issue #13041 · conda/conda · GitHub.