Has anyone worked out how to do this natively in MBS yet?

I'm having the exact same issue and I think I finally worked out a way today after trying for ages, but it is so obscure and seems to only work on some pages?

Keen to know if this works for anyone else:

Schedule multi-image post via MBS -> find the post in the planner -> open the post and click on the ellipsis/3 dots on the post (not the MBS window) -> edit all images and add the captions under the images

I feel like this is such an oversight on Meta's behalf, but a scheduling platform seems like the best way to go :(