Maybe the monitor doesnt support a higher refresb rate?

what 4k monitor doesnt support 30hz at 1080p?

From the specs it should do 4k@60. At 1080p it would be madness if it could not drive at 60.

yeah… macbooks for you…

Mine works fine at 2x 1440p144hz. Even my old loaner MacBook did fine at 1x 1440p144hz and 1x 1440p60hz, though that was a relatively old laptop (mid 2017).