to answer the OP question (answered in other subjects), folders require frame strengthening due to the hinge mechanisms, the more hinges, arguably the heavier. So the frameset is limiting. Now, yes, there are lighter weight frame but they are low volume so expensive and expensive = less sales so vicious circle.
Then the folders are supposed to be "economical"; unlike race bike or high end MTB, there are less people willing to spend loads of cash on folder so, the manufacturer do not assembled them which top of the range groupset (few Sram Red or Shimano Duraace etc.)
Then, the manufacturer have to mix and match things to give a 20" similar range/gearinch to a 27.5" or 29".
So, if you considered the budget gravel/road bike, aluminium frame fitted with similar groupset, the weight or 20" is pretty similar 10-12kg.
If OP wants a 8-9kg bike, OP will have to start from a lighter frame and then fit premium groupset, descent wheels like Dahon/Tern Kinetix pro (Chinese carbon don't seem to be super light) and fit light weight seatpost and faster basically, weight winny game and this is very custom and pricey.
I my experience, the sweet spot for [weight vs price vs part availability vs low maintenance] is 9.5 to 10.5kg. It is easily achievable when starting from a 12-13kg std commuter bike.