Related to this, I would like to be able to save an element as a component, then apply default styles or settings to that component, which can then be used in other designs. Changes made to the component can be applied to instances within different designs, but instances can also be detached or overridden - similar to Figma's components.

I just figured out a slightly complicated workaround but yes, this would be a great feature to make it easier since this has been a very popular feature in v3. The workaround is as such: Using the right click menu (which takes a few right clicks to override my computer/browser's default right click menu), I thought, what if I try to copy the entire container with the elements from promo A and drop it into a new frame inside promo B...and it worked. That said, an easier/permanent link-between designs feature would be better for other situations where this happens, but good to know the copy/paste works outside of the current promo I'm in for last-minute changes as well.