This is the best I've seen in the last 1-2 years: https://www.matadorequipment.com/pro...kable-backpack
I don't have direct experience, but have been on the lookout for viable replacements for my excellent foldable backpack that will eventually give out after 10+ years of hard service.

If you're in the NYC area, I saw it at the MoMA store in soho some months ago. I am not sure how well it will work for you. The material felt a little flimsy but will probably carry 5-7kg, and the straps had some padding although I wouldn't call it well-padded. Both are tradeoffs to get it collapse compactly.