Hi,
The error messages have been reported before here on discourse and on GitHub.
It seems to be a bug related to an interaction between homebrew and jupyter. You can probably ameliorate them by setting environment variables before running jupyter:
JUPYTER_PATH=/opt/homebrew/share/jupyter JUPYTER_CONFIG_PATH=/opt/homebrew/etc/jupyter jupyter notebook
The changed appearance is a feature of notebook 7. If you prefer the old appearance, use nbclassic instead of notebook.