It looks like #HaloCampaignEvolved relies exclusively on Hardware Lumen for its Global Illumination and Reflections, with no Software Lumen fallback. I did a quick test on the 3060 Ti by disabling the “Raytracing (DXR)” flag in NVIDIA Profile Inspector, which basically disables the GPU's ray tracing support. This gives a significant performance boost, but it completely disables the game’s Lumen GI and Reflections.
So even though the game uses Hardware Lumen, it can still run on non-RT GPUs, albeit with substantially degraded visuals.