Translucent blend mode is still very much in 5.4. It’s just not available in Substrate, which you appear to have enabled if you’re seeing the alternative blend modes.
Substrate is still experimental and may have some missing feature support. You may want to check the Feedback Thread for it. If you do post an issue you’re going to need to supply more information about the issue, Unreal has lots of raytracing features and it’s not clear which one you’re talking about here (path tracing maybe?)