Hello.
I'm playing the game right now and it definitely does use s/w Lumen for GI and reflections. Granted GI seems quite a bit limited in this one (sky light only and seemingly only for some surfaces) but there are obvious "boiling" artifacts you get from your typical s/w Lumen lighting. The game doesn't allow you to disable Lumen GI as the setting for GI which does that in UE5 is limited to "medium" being the lowest possible option - you'd need to set it to "low" to disable GI completely.
There are also your typical s/w Lumen reflections, easily noticeable on the frozen pond at the end of chapter 1. Here the setting for reflections goes down to "low" (no reflections) then "medium" (SSR only) and "high" and "cinematic" (s/w Lumen SDF tracing for out of screen objects covered with SSR for on screen ones). This could be a cube map fallback but since UE5 doesn't provide these I'd just go with the easiest possible option of s/w Lumen SDF tracing.