Reviewed June 3, 2022
When in Edit mode, there is no obvious way to expand the container to view or edit its contents--clicking the container merely controls editing the container's settings.
This is normal functionality for Flex UI. Expanding a collapsible content container is a page function, not an edit function.
Switch to Preview mode and expand the container, then return to Edit mode to view or make changes to the contents.
To speed up this process, use the keyboard shortcut Ctrl-Shift-m to toggle between modes, or just select the container and use the "x" one-key shortcut.
And if you have multiple containers on the page, you may wish to expand them all in one go to save time.