I think Canva Pro might do this - I dunno, I'm not paying for it.

You can certainly ask ChatGPT for a poster, then ask it for a collection of assets with transparency, so you can composite them as you wish.

It does take away from the "smash out a poster in 10 minutes" that a harried PTA volunteer wants, though.

I suspect the tool to do this as a one-stop shop is coming very soon, though.