Coincidentially I was working on a similar topic to analyse the status of the Dark Mode stylesheets.
The way I triggered this situation was as follows:
* Close the current Leo instance & rename directory ~/leo to ~/oel
* Start a new instance of Leo
* Enter 'tmp' as the temporary Leo ID
* Create the attached screenshot
* Fall back to the working setup by deleting the newly created directory ~/leo & renaming the 'old' directory ~/oel to ~/leo again ...
Please let me know if you need anything else in that state ...
With kind regards,
Viktor