on one specific notebook that is jupytext-encoded in Python
apparenty this is a long shot; see a message by @bollwyvl on gitter.im in the jupyterlab/jupyterlab room on 2024 Apr 26
he seems to imply that server-side extensions need to be rewritten in js...
so right now this opens as a text file...
notebooklite - Unknown Directive
notebooklite - Unknown Directive:width: 100% :height: 500px :prompt: a jupytext notebook :prompt_color: aquamarine
so a fortiori this won’t work inside a dropdown..