In Notion and Anytype everything is a “block”. Fibery hasn’t fully embraced this in the UI, much to my disappointment, but as you can see with the recent addition of “Drag to Reorder Elements”, most things in Fibery are “blocks” too! So why not have a toggle on every block? No, not one that is visible all the time, just on-hover, like the Block Handles in Notion. Maybe it becomes “sticky” visible in collapsed state. So you could toggle any Heading, sure, but also a any level of a bullet list (a separate feature request in itself), or an in-line Table, or a code block, or an embed. Anything that is taking up too much space. The point of it is basically this: most often I see people putting things they want to collapse “inside” of toggle-able blocks. But, for example, often I did not want a header or toggle there, I just wanted to collapse some embed(s) or something. But I had to make a toggle block in order to collapse what I actually wanted to collapse. Toggle on all blocks solves this elegantly IMHO.
This would probably require Fibery more deeply embrace “blockness” to really work well though.
All this would be great one day, though I have doubts it will happen any time soon, if ever. But since Fibery is already able to address many discreet pieces of Rich Text as “blocks”, why not make them all toggleable at least? Doing so does not require all the other fancier features of blocks.