Use DSR at lower than native resolution?

I don't think this is possible but just double checking.... monitor does 4k@30hz or 1080p@120hz, I want to use DSR to render at >1080p and still output 1080p. But options seem to only allow scaling down to native resolution.

Double checking I cannot get GPU to render at 4k and output 1080p.

Yeah, DSR only works when the internal resolution is higher than your monitors maximum resolution.