That is correct , I am not staff.
I suggest you share your read-only project on your initial post. Then open a ticket with Webflow and reference this topic URI. I moved the ticket to BUGS to help you get visibility.
I will say that I never try to drag assets from Explorer to the canvas. I always open the asset panel, drag them there, then from that to the designer canvas.
Things you will probably be asked;
Have you tried incognito mode?
Also what is the max size of the files you are attempting to upload?
FYI: I tested dragging in 6 images to the designer asset panel via WorldStream B.V. in the Netherlands and had no issue. Same Browser / build / OS.
Good luck resolving your issue .