I’m running into this same issue, and I wanted to use the cheap glass material I had created in UE5. Unfortunately the cheap glass material tutorials I found required an HDRI itexture to fake the reflections 
Not sure if we actually are able to create our own cheap glass materials in UEFN, because HDRI textures are not supported?
Have you been able to? Translucent materials are super expensive and I have an entire wall of glass windows in my shop. When I created translucent glass in UE5 and used the Optimization view to check the Shader Complexity my whole wall lit up bright red. The UE5 material I want to use is Additive, or it works with Modulate too.
@AxelCapek I think I’ve heard you request support for HDRI images for cubemaps, right? Is there a post about this that I can upvote?