Dual monitor 4K and 1920x1080 settings

I have a 4K ( HiDPI) monitor and a 1920x1080 monitor.
How can I set the size for the 1920x1080 screen because fonts and frames are to big for applications like the gimp , inkscape etc.

Just an idea: you could split the difference in sizes between resolutions by running the 4k display in 2k mode, 2560x1440 (using xrandr --output <outputname> --mode 2560x1440 in an X startup script). You could also try the reverse, scaling up the 1920x1080 screen to 2560x1440 (using xrandr --output <outputname> --mode 1920x1080 --scale-from 2560x1440 in an X startup script). You might even try both.

I have setup the first 4K monitor with these settings
https://en.opensuse.org/High_DPI ( fonts dpi is 192 ).
Now the applications opening on the second screen are to big.
My second screen cannot set higher then 1920x1080 graphic tablet.
It has a 22" IPS panel.

Scaling means using an available/supported mode to shrink everything from a higher resolution to fit a lower resolution:

# grep -v ^\# /etc/X11/xinit/xinitrc.d/setup | grep xrandr
**xrandr** --dpi 120** --output HDMI-1 --mode 1920x1080 --scale-from 2560x1440** # DP
# xrdb -query | grep dpi
# xrandr | egrep 'onnect|creen|\*' | grep -v disconn | sort -r
Screen 0: minimum 320 x 200, **current 5120 x 1440**, maximum 16384 x 16384
**HDMI-1 connected 2560x1440**+2560+0 (normal left inverted right x axis y axis) 700mm x 390mm
**DP-1 connected 2560x1440**+0+0 (normal left inverted right x axis y axis) 598mm x 336mm
   **2560x1440**     59.95*+  74.92
   ***1920x1080***     60.00*+  60.00    50.00    59.94    59.93
# xdpyinfo | egrep 'dimen|ution'
  dimensions:    **5120x1440** pixels (1083x304 millimeters)     # 5120 = 2560 * 2
  resolution:    120x120 dots per inch
# inxi -GIMSay
  Host: ara88 Kernel: 5.3.18-lp152.44-default x86_64 bits: 64 compiler: gcc v: 7.5.0
  parameters: BOOT_IMAGE=/boot/vmlinuz noresume mitigations=auto consoleblank=0
  radeon.cik_support=0 amdgpu.cik_support=1 video=1440x900@60
  Desktop: Trinity R14.0.8 tk: Qt 3.5.0 info: kicker wm: Twin 3.0 dm: TDM
  **Distro: openSUSE Leap 15.2**
  Type: Desktop Mobo: ASRock model: FM2A88X Extreme6+ serial: E80-38024200616
  UEFI: American Megatrends v: P4.20 date: 01/13/2016
  Device-1: AMD Kaveri [Radeon R7 Graphics] vendor: ASRock driver: amdgpu
  v: kernel alternate: radeon bus ID: 00:01.0 chip ID: 1002:1313
  Display: server: X.Org 1.20.3 driver: modesetting display ID: :0 screens: 1
  **Screen-1: 0 s-res: 5120x1440** s-dpi: 120 s-size: 1083x304mm (42.6x12.0")
  s-diag: 1125mm (44.3")
  Monitor-1: **DP-1 res: 2560x1440** hz: 60 dpi: 109 size: 598x336mm (23.5x13.2")
  diag: 686mm (27")
  Monitor-2: **HDMI-1 res: 2560x1440** hz: 60 dpi: 93 size: 700x390mm (27.6x15.4")
  diag: 801mm (31.5")
  OpenGL: renderer: AMD KAVERI (DRM 3.33.0 5.3.18-lp152.44-default LLVM 9.0.1)
  v: 4.5 Mesa 19.3.4 direct render: Yes
Info:...running in: konsole **inxi: 3.1.07**

Well if the answer is shrink everything to a lower resolution then I change my resolution for the 4K screen
back to 2560 x 1440. Unfortunately no good 4K support with Leap 52.
By the way I have a AMD RX580 8 gb (graphic card) with amd repositories (manually added) for openCL-support.
Default you get a black screen but I am used to the poor graphic support due licenses.

Long ago I had one 4K and one WUXGA (1920 x 1200) and got a sort of solution running a small xrandr script. If you havent’t already seen the thread it maygive you some ideas: