In the right-hand column in Gutenberg, my nested Flexible Content Fields don’t collapse… clicking the triangle icon does nothing.
The parent (outer-most) flex content field DOES collapse, but not the inner/nested one.
I’ve not gone deeper to look into it to investigate.
I note that this is also the case for the main editing area – no collapsing of the internal flex content fields either.
Click-and-drag of the inner/nested flex content fields also doesn’t work.
Same issue, no doubt.