Background scrolling instead of cart

I can’t be the only one experiencing that issue with the cart wrapper stuck on mobile portrait.
I find solutions here for the issue in general but the cart differs from these (as explained above).
Either I’m not explaining myself correctly or I’m not getting the obvious, or it’s just one little thing I’m missing, one element that needs to be changed… I just can’t figure it out.
Frustrating!
Help would be highly appreciated! Thank you!