I’m seeing some issues with the Python extension opening notebooks as of this weekend. These issues were resolved in the latest versions of the extension (see https://github.com/eclipse-theia/theia/issues/3186). However, I now get the '‘No available file system provider for schema file’ error also reported here: https://github.com/eclipse-theia/theia/issues/8022. You can reproduce by trying to open the notebook in this Gitpod: https://gitpod.io/#https://github.com/intro-to-geoprocessing/week6-lab.
If I look in the built-in extensions list, the installed version of the Python extension seems to be 2019.11.50794 while the most recent version on Open VSX is 2020.9.112786. Other built-in extensions also seem to be older versions.