Shift + Tab tooltips not showing in JupyterLab 4.2.0 / Python 3.12.3 (pyenv) on Ubuntu 24

SHIFT + TAB tooltips are not showing for me in my fresh Jupyterlab install.

Platform: Python 3.12.3 (via pyenv) on Ubuntu 24.04.

Here's the output of $ jupyter --version:

Selected Jupyter core packages...IPython          : 8.24.0ipykernel        : 6.29.4ipywidgets       : not installedjupyter_client   : 8.6.1jupyter_core     : 5.7.2jupyter_server   : 2.14.0jupyterlab       : 4.2.0nbclient         : 0.10.0nbconvert        : 7.16.4nbformat         : 5.10.4notebook         : not installedqtconsole        : not installedtraitlets        : 5.14.3

• I have already imported the module I want to get tooltips for, so that's not the issue here.

• Also, I don't want to get tooltips from within some convoluted expression (e.g. asking for a tooltip from requests.get(url) doesn't work).

• I tried two different browsers, no luck.

• I also tried uninstalling jedi as suggested here, no luck.

• I also have Jupyterlab in my Python 3.8 (also pyenv) and SHIFT + TAB works fine there.

Any ideas what else to try?

NOTE: There are a bunch of questions (one, two, three) asking more or less the same, but none of them have answers that work for me & all are missing version / platform info, which is probably relevant.