Cloud providers that offer Mac mini servers use a HDMI dummy plug to emulate the presence of a display, but macOS will usually not treat it as a HiDPI display. This project is great for creating 4k screenshots on such servers.
(I have 4k screen and need to scale up the text size to 2560*1440. Then I found these app only take the 2560 screen to remote)
The best remote experience I have had with macOS is using the built in VNC, but not with a standard client. Using the Remotix client provides a great experience. It's $50.
I have also heard that NoMachine for macOS works really well, but I have not tried it.