KDE desktop styling and usability problems

Application UI scaling was a previous note on the problem of fonts on the KDE desktop, but this is an attempt to document exactly what I AM seeing.

The starting point with all this was the high resolution monitor that I switched to as the four 27" HD monitors were no longer available. It was augmented by a 19" HD monitor, but that just seemed to confound things, so having saved up a little money, a second reconditioned 32" 4k monitor now sits in it's place. Yet still things are proving to be difficult. I KNOW that the starting point should be to simply wipe everything back to default, but just how precisely does one do that? In X11 I have a global scale option on the Display & Monitor Display Configuration page which modifies both monitors, while on wayland each is changed separately. Currently I have all back at 100% along with switching off the font DPI override in X11. That one does not appear in wayland. Is there anything else that needs to be cleared to give a base to work from? Not sure, but at least this is a starting point.

So now I should be able to set a suitable font size for the screen size? On wayland I've just changed from 10pt to 12pt and the screen font went DOWN is size, so need to compare that action with X11. Time to save this and re-log in. I really must look and see if I can recable the two displays since while logged out they are the wrong way around! Anyway now back in on X11 and after changing away from 12pt and back I seem to have the same font size as under wayland. A start at least. An more important, I can actually read the text around the firefox window such as the tabs. THAT has been a problem with wayland which I need to go back and cross check ... however in Thunderbird I have to set the font option to 24pt to get something similar to the 12pt in other windows. The major problem IN Thunderbird is, as with other applications, pop-up windows like search messages open up with a font half the size of that in the main window. So where exactly is this getting broken?

Going to head out for a bit so back to this latter when I'll go through a few more of the problem apps and see what the starting point is there ... then cross check with wayland. One that may be a problem is KiCAD which has already put it's hand up to the fact that things it relies on to function as it does are deliberatly removed in wayland, so I should stay with X11 anyway to maintain a key factility I have built a lot of designs on in the past.