I have an application that spawns many windows, and I cannot at the moment use
xpra as is required by the accepted run_scaled solution. I also can't tolerate gnome-tweak-tool's 2x scaling. Too huge. Need 1.5x.
I have discovered that the tigerVNC java client supports client-side display scaling of 150%.
So I start a vncserver with 2/3rds size and a minimal windows manager:
vncserver -geometry 2520x1380 -xstartup ~/.vnc/xstartup-mwm
I then connect with TigerVNC's v1.7 java client (1.8.0 consistently crashes for me):
java -jar VncViewer-1.7.0.jar -ScalingFactor=150
Other than the commandline, you can hit
F8 to get the VNC Viewer Options. Screen->Scaling Factor->150%. This scales the resolution from 2/3rds of 4k to 4k.
Archaic MWM in VNC with 150% scaling on the left. Fancy Gnome desktop (native) on the right, no scaling. You'll notice the tiny icons. Gnome is otherwise adjusted for 4k with 1.5x Font Scaling in gnome-tweak-tool, but the icons don't scale. This is just an example application -- the icons and scaling in the application that is pushing me this way are far worse.
Unfortunately this is an entire 1.5x scaled desktop with a separate window manager. It creates a nice walled-off area for my multiwindow app, but it's annoying to have a second window manager. Nonetheless VNC is something I'm familiar with from longtime use, and this does kick over to the laptop pretty easily, so perhaps this is usable.