Code folding broken in 4.0.0a28+?

Hi, is that only me or is code folding broken in the recent jupyter lab pre-releases? I didn’t find an issue, though.

If I activate code folding in the new settings editor (Notebook->Code Cell Configuration->Code Folding), the extra bar left of the code cell (where the triangles are supposed to appear) is there, but no triangles to let me collapse functions.
Peek 2022-10-15 15-42