Mac M1, no gui

```
192 ~ % julia
_
_ _ _(_)_ | Documentation: https://docs.julialang.org
(_) | (_) (_) |
_ _ _| |_ __ _ | Type "?" for help, "]?" for Pkg help.
| | | | | | |/ _` | |
| | |_| | | | (_| | | Version 1.7.0 (2021-11-30)
_/ |\__'_|_|_|\__'_| | Official https://julialang.org/ release
|__/ |

julia> using PyPlot
[ Info: Installing pyqt package to avoid buggy tkagg backend.
[ Info: Installing PyQt5 via the Conda pyqt package...
[ Info: Running `conda install -y pyqt` in root environment
Collecting package metadata (current_repodata.json): done
Solving environment: failed with initial frozen solve. Retrying with flexible solve.
Collecting package metadata (repodata.json): done
Solving environment: failed with initial frozen solve. Retrying with flexible solve.

PackagesNotFoundError: The following packages are not available from current channels:

- pyqt

Current channels:

- https://conda.anaconda.org/conda-forge/osx-arm64
- https://conda.anaconda.org/conda-forge/noarch

To search for alternate channels that may provide the conda package you're
looking for, navigate to

https://anaconda.org

and use the search bar at the top of the page.

julia> versioninfo()
Julia Version 1.7.0
Commit 3bf9d17731 (2021-11-30 12:12 UTC)
Platform Info:
OS: macOS (arm64-apple-darwin21.1.0)
CPU: Apple M1
WORD_SIZE: 64
LIBM: libopenlibm
LLVM: libLLVM-12.0.1 (ORCJIT, cyclone)
```

Any known workarounds?

Reproduce the failure in the Julia REPL with PyPlot on macOS arm64 using Julia 1.7.0, then inspect the PyQt5 installation and matplotlib backend setup reported in the issue. Done means the GUI opens successfully or a confirmed workaround is documented for Apple M1 systems.

Written by the indexing model from the issue text.