Do you care more about visuals or performance?
Visuals: go 4K HDR, but don’t go cheap on it. A lot of 4K HDR monitors aren’t really HDR at all and will look super washed out.
Performance: 120hz refresh rate. This is probably going to be the “new 60fps” in the coming years, and future proofing for that is smart. A 4K monitor that runs a 120hz refresh rate though is very expensive right now, so go for 1440p or 1080p. You’ll lose visual fidelity and color pop that, IMO, is a major difference, but 120fps is so very, very smooth.
But as @GhostofDelta2 said, it all depends on what your PC is capable of. You won’t see an upgrade if you don’t have a GPU that can handle the higher output.