Similarly to the product description read more option, but can be enabled for any text block element.
Alternatively, a "Read More Text Block" that's separate from the main one.
Thank you Ben for the feedback. Actually this feature has been released in the new Editor V7, if you still using V6 you can try to request the CS team to let them upgrade it for you.
It totally makes sense if we can to expand or collapse the content inside for Text Block like we can with (P) Description.
We'll gather around and have a plan for it.