Progressive GPU changing to CPU

When I try to bake my scene lighting with Progressive GPU selected, it waits a couple of minutes, and then switches to Progressive GPU. I have an NVIDIA GeForce GT 730, AMD Ryzen 5, 8GB DDR4 RAM. It usually takes about 5 minutes to bake my scene with medium settings on CPU.

uhm hello

Unity will fall back on the CPU if your GPU rans out of VRam.
it says so here in the third note.

Note: If the baking process uses more than the available GPU memory, the process might fall back to the CPU Lightmapper. Some graphics drivers with virtual memory support swap to CPU memory instead, which makes the baking process slower.
Unity - Manual: The Progressive GPU Lightmapper (preview)

Now a NVIDIA GT 730 is a 7 year old low end GPU.
They Have either 2GB or 1 GB of VRAM.
there is 1 4GB one.

The Docs Says you need at least 2Gb of Vram.
the GPU also needs OpenCL 1.2 support. The 700 series supports this.
A Ryzen CPU definitely supports SSE4.1 .
if you have the 1GB version you will run out of VRAM very quickly. the 2GB will last alot longer but I’d imagine it will still give out eventually, since that memory is being shared with the Editor, Scene and other applications.

I don’t work for unity but I’d have a very strong guess Unity tries to use the GPU because you ask it to, quickly eats through the V Ram and then switches to stop the GPU from Crashing.