Did any of the examples you’ve found where jupyter-server-proxy runs include JupyterLab 3? I see given the ‘Bump extension to 2.1.2: jupyterlab 3 support’ comment text of this commit that they’ve done it; however, given that commit was last month and JupyterLab release candidate only very recently was shown to be Binder-ready I’d like to find a working example via Binder before switching from JupyterLab 2 to 3. Seen any?
Did you try putting a trailing / after 5000? It used to be very important, see the bottom of GitHub - chekos/testing-streamlit-mybinder: A repo tryna see if you could run a streamlit app in mybinder . I think though it was adjusted to not be required because I seem to have a mix.