Adjusting font size not always possible

I'm not sure if something has changed in Windows 11 or more likely my personal memory chips are faulty and I'm just not remembering things.A few weeks ago carried out a clean reinstall. All went as expected and then I set about the rest of the necessary work, drivers, apps.
However I am left with one issue which may be my faulty recollection or I have missed something. A lot of apps have very small fonts, look like 8 or so. In many of the apps it is possible to enlarge them. Some apps don't have the option. Outlook is a bit of a mix. The reading pane can only be adjusted via the slider at the bottom of the screen, but the default is small and I have to increase it every time I want to read or create a message. The other panes can be adjusted and set individually, Message boxes however are all tiny - looks like font size 8.
I have adjusted all the Windows settings I can find that alter font size. Same for apps were available. I have looked at a few things on the Nvidia control but the only thing that resolved the problem was changing the resolution of the larger VD which is obviously a bit pointless as I lose graphic workspace.
The other thing which is not as I remember pre-reinstall is if I drag an app from one screen to another, then text is fine in the lower res VDU but too small in the higher res one.
Setup is Windows 11 (whichever one downloaded itself last night)
Graphic card Nvidia Geoforce GTX 1600
VDUs - Both BenQ - 3840 x 2160 and 2560 x 1440

Any thoughts welcome!

I can't offer a lot of advice. I never have been able to get consistent font sizes in all areas of windows. Some apps have certain areas hardcoded which takes preference over any user settings. To make the fonts in those areas large enough for our old eyes to read, you have to enlarge scale to the point it throws everything else out of whack. (for instance control panel) Same goes for third party apps and some websites. They hardcode certain areas as well. I've had to experiment with my scale, font settings, system font, resolution, and zoom level in browsers to reach an acceptable medium. Keep in mind, the higher the resolution, the smaller the font. So if you use 1 screen to reach your happy medium and then connect another monitor with a higher resolution, you might not be as happy until you tweak your settings again.

I don't know about your graphics driver but ever time I get a new driver I have to reset my scale and resolution changes again.

Regarding Outlook, if you use MS Office Outlook you have more options. Outlook on the web, not so much.

In a search this "old" message/post came up first, so my reply is mainly to the font size not remaining as set after rebooting.
Have tried several ways to set the text/font size as read at microsoft "help" pages, yet none of those methods kept the text/font in my windows explorers set to the size I preferred after rebooting. After rebooting the text went back to default (ᵗᵒᵒ ˢᵐᵃˡˡ ᶠᵒʳ ᵐʸ ᵛᶦˢᶦᵒⁿ) size.
I used an old win98 style of going to the deepest folder of the active user and once there created a blank txt file.
Before creating the text file deep into ACTIVE USERS folders level, I opened FIRST the DISPLAY>SCALE, set it back to 100. (even if its at 100 move it so one gets that message to restart the computer, BUT DON'T RESTART YET. Had it at the DISPLAY>SCALE at 138, which did maintain the text at a decent (FOR ME) size but since the SCALE settings change the size of ALL, app interfaces and toolbars where getting too close to not displaying correctly or fully.)
After setting DISPLAY>SCALE to 100 I then changed the TEXT SIZE slide bar to 150%. Saw the size of the text in the folder's names become nice and large. Opened the txt file, wrote gibberish into the txt file, closed it but then reopned that txt file and left that open and document folder open.
In Win98SE this trick (IN SOME assembly line manufactured MODELS, not customized models) for some reason forced the registry to maintain (unless one changed it) the matching last settings (order of files, size of text, colum choices) of txt and deep level opened folder.
THEN I clicked on the restart choice the DISPLAY>SCALE offered when I had changed it to 100%.
The computer rebooted and have turned it off and on three times (last 6 hrs) and the larger text is still holding. (fingers crossed...which might explain my misspellings).

If the text looks too small, go to font size, move the slider to whatever percentage you prefer, click apply. Once Windows sets it, move the slider back to the default 100%. Now click apply again and wait for Windows to finish setting it.

Now your text should be normal again.