I have the same problem, my UE 5.3 created a shadow for opacity materials, UE 5.4.4. does not anymore. No settings changed, just updated the map to a copy to 5.4.4.
I can make a level from scratch and add a opaque object, no shadow no matter how much I klick on everything and anything
- Picture is UE 5.4.4. Ignore filename, I did not change the name to 5.4