I’m super late to the party, but I recently discovered Alpa. Several sizes of an awesome super lightweight/collapsible backpack with a trolley sleeve. Best part IMO is that it opens up to 2 pack able sides like a suitcase- not 1 large one like a normal backpack. See what I mean in the photos:
https://www.cotopaxi.com/products/allpa-35l-travel-pack-4
https://www.cotopaxi.com/collections/allpa-travel-packs
I’ve been trying to find a cheaper alternative but after several hours of research this seems to be the only pack that checks all the boxes for myself: lightweight so u can pack it empty in a suitcase, fills out the maximum carryon measurement requirement, has trolley sleeve, easy to pack interior.