I figured I’d put this here as I’m not seeing any specific release notes that make note of it or mention the loss of lumen in 5.5 dx11.
5.5 no longer supports lumen in DX11 with SM5 which is a huge loss in my honest opinion because it was by far the most performant GI supported pipeline with traditional LODs vs nanite and a lighter weight shader cost and shadow casting (CSM). In order to have Lumen GI (as of 5.5 release) now you have to enable SM6 and DX12.
UE5.5 DX11 (No longer working)
UE5.5 DX12 SM6 CSM instead of VSM
20+ frames lost just for GI
Update:
After some digging it appears the 5.5 docs still mention DX11 and SM5 however in the feedback thread below an epic staff member said it was deprecated?
Lumen GI and Reflections feedback thread - Development / Rendering - Epic Developer Community Forums
I do a much better job of breaking out DX11, SM5 and DX12 across each shader model in the below forum post. This is a huge loss in my opinion and directly impacts many studio and orgs business models.
Lumen no longer working in UE5.5 DX11 SM5 - Development / Rendering - Epic Developer Community Forums