Is this a known issue?
Temporary?
Something on my end?
Ref: upload of a 1024 x 1024 png image for an app Icon.
Tried many different file sizes.
We don't know - you don't tell/show us what your are attempting.
I am attempting to Upload a 1024 x 1024 png image for an app Icon.
Probably a temporary issue at your end. Reload your browser/AppInventor and try again.
I might suggest you resize/reformat your icon image to 512x512 as a jpg.
Works using Edge, must not like the Opra browser.