Hi all,
Just update for those who is experiencing same issue.
Version 1.8.0 Alpha did not solve this issue (not that I expected that reading release notes)
I also learned that macOS does not really scale 1080p very well, so I upgraded my monitor to 1440p (27" LG ultragear 27GN880) and it looks way, way better.
Still only 60hz though, (yes with hdmi 2.0 cable) and when I connect my monitor with another dongle (usb-c to dp) I get 1440p variable refresh rate
I hope that one day there will be an update that will fix this.