Fractional fonts and icons?

Is there a way to move font size handling away from pixels to a fraction of current screen-height? My (mostly dayligt use) laptip is 1920x1080 and my (mostly evenings) desktop is 4k and for ballpark guidance I would be looking for 1/30 of screen height and splay derivatives around that fraction. How would I set this up with currently available preferences?

Let me begin on the left deskbar where I have very little control over SystemTray icons which I would like to group much the same way as the quick launchers ..but can’t, meaning they take up more that about 150% of what they should in PRIME CONTROL-PANEL REAL ESTATE.

Then, next to it to the right is a KDE fonts dialog which throws me: the ‘force-font-dpi’ checkbox needs to be checked for the annunciation to the effect that ‘global’ resizing is the way to go instead. But then the ‘do global resizing’ button is also invisible unless the presumably incompatible ‘force-font-dpi’ check box is checked. I get confused, how to set up global factoring without forcing font-dpi?

Finally, the real headache!!! How to set up so that the mix of apps I use will all have approximately the same 1/30 of screen height fonts spec, 1/40 to maybe 1/25 which on my 1080 laptop would revolve around 36 and 72 on my desktop. Observe some of the title-bar fonts in the screenshot even though I have 200% global zoom set, also the firefox horror that google puts up even though I have font size 9 in its prefs.

If anyone has a workable solution I’d sure like to duplicate it. TIA

plasma doesnt really size fonts as a fraction of screen height. closest is force font dpi + global scale, tuned per machine.

1080p laptop:
-display → global scale ~100-125%
-fonts → check force font dpi, start around 96-110 and bump til it feels right

4k box same menus, usually higher scale (150-200%) and dpi around 144+

tray eating the panel:
-right click panel → configure panel → height
-system tray → configure → entries (hide what you dont need)

force font dpi is the global resize path. that other apply button just pushes the dpi you set.

What I was thinking of is a new global reference that all userspace software then would use. I know KDE doesn’t do this, no one does.

For now I just looked into the force-font-dpi button which is supposed affect all applications uniformly. I saw about 108 in there and then read that setting this was equivalent to editing .Xresources to show Xft.dpi: 108. Problem is that .Xresources was showing 200 while the laptop (a 1920x1080) has a monitor with 157, I have no idea where that 200 came from. Things improved somewhat after editing that file and the kde force-font-dpi to this hardware spec of 157. Is this monitor spec automatically detected (as I would presume)?