@pparent When you install Ubuntu Touch on the Fairphone 4, everything is default setting. UT Tweak Tool shows scaling 21. The text size is about 0.8mm for characters like aceimnosruvwxz. It is small. Heading size is about 1.8-2mm, which starts to be easier to read.
Not everyone has super sharp eyes to read the back of a mobile charger print or the ingredient list on the back of a small product. If Ubuntu Touch should be usable by those who use reading glasses, it has to, by force be able to scale all the different text sizes and icon sizes individually. Android phones have this global adjustable font setting with biggest size around 6-7mm. Doro phones even bigger sizes, and big icons for clumsy fingers. Children tend to like bigger buttons as well. Look at the Gameboy Emulator. It has big buttons even on Fairphone 4.
The default scaling 21 allows for 4 app columns in the drawer portrait mode. This should be good for most people, but it is too small. Medium size on Android is bigger.
On Android you usually have 3 steps from medium to the extreme, which is where Ubuntu Touch is default. So, medium size is 3 steps up from where it is now, at 21 scaling, and HUGE is 6 steps up from now.
Scaling 24 allows for .3 app columns in the drawer. But the text is still too small.
Scaling 27-30 allows 2 columns in app drawer portrait mode. But headings fall outside screen to the right. The PPI of a screen (400) correlates with the scaling I guess and the result is a font height in pt or mm. Most text in LibreOffice documents is 10-14pt big. Firefox text has to almost always be scaled 1.2-1.33 on 1920x1080 monitors 15 inch big. An older laptop with lower screen resolution does not always need to scale the text in Firefox. The text is automatically bigger if the resolution is smaller. Ubuntu GNOME out of the box on a 4K display has small text. Usually everything has to be scaled 2x on 4K monitors.
The worse eyes need a bigger text, sometimes a medium font thickness (600). Bookerly font versus Times illustrates this need. Thin font with small size is difficult for worse eyes. We want our grandmas to use Ubuntu Touch, so... we have to re-program Ubuntu Touch to allow global font settings => qt font settings. I am afraid it is absolutely necessary to adress the font size adjustment need.
I managed to click on a cog wheel and on the right side, there is a box zoom: 100%. It does not work and it is difficult to even see the settings. Pulling out a PS2 keyboard and connecting it via USB, Ctrl ++ twice usually make the text a bit bigger. One should not have to connect a keyboard to zoom. So the scaling is already there, its just difficult to do it via the cog wheel in Signal (Settings).
I purposely use everything default on Ubuntu Touch to see how things scale. Terminal allows to have a big font for instance. But many apps just stick to default set by the system, which is too small. I use Fairphone 4 because it has USB3 for external wired monitor. It has a great screen PPI of 400. I cannot change that. But I wish to be able to read the text in Ubuntu Touch and be able to scale it up when needed.