Just fflags for the client itself. I also have a GTX 1660 SUPER so due to this the client just defaults to using that card instead. I have to force it via fflags to use vulkan which just so happens to default on my B580. Vulkan also yields quite substantially higher framerates on my B580. Issue does not happen with studio so im not sure if this is the result of some fflag shenanigans or something else. Most i know is that vulkan on the client is very unstable.