Is there a way to enable HiDPI scaling for external monitors on MacOS? https://www.macrumors.com/2016/09/23/loss-of-resolution-scaling-macos-sierra-update/

Is there a workaround to get HiDPI mode on external monitors on macOS Sierra?
Use SwitchResX. It allows you to enable HiDPI mode. It also offers the possibility of "faking" a HiDPI mode by scaling (I use a fake 1080p HiDPI on my 2K thunderbolt display). No remarkable performance issues reported.