I did search and do a script:
$cat ./xrandr cvt 3840 2160 59.91 xrandr --newmode "4K" 711.75 3840 4160 4576 5312 2160 2163 2168 2237 -hsync +vsync xrandr --addmode XWAYLAND1 4K xrandr --output XWAYLAND1 --mode 4K`
But now even that in the settings-->devices-->screen resolution I did not have a 3840x2160 mode to choose in the list.
When I run my script:
$ bash -x ./xrandr
+ cvt 3840 2160 59.91
# 3840x2160 59.90 Hz (CVT) hsync: 133.99 kHz; pclk: 711.75 MHz
Modeline "3840x2160_59.91" 711.75 3840 4160 4576 5312 2160 2163 2168 2237 -hsync +vsync
+ xrandr --newmode 4K 711.75 3840 4160 4576 5312 2160 2163 2168 2237 -hsync +vsync
X Error of failed request: BadName (named color or font does not exist)
Major opcode of failed request: 140 (RANDR)
Minor opcode of failed request: 16 (RRCreateMode)
Serial number of failed request: 18
Current serial number in output stream: 18
+ xrandr --addmode XWAYLAND1 4K
+ xrandr --output XWAYLAND1 --mode 4K
xrandr: Configure crtc 0 failed
What is the solution for that? I have Ubuntu 17.10. I had this resolution earlier...it just disappear.