Stepan Konev

Check the setting in Windows for the view magnification. I have never seen Studio behaving that way...

Thank you Jerzy for your input, 
but I don't think I know what is 'view magnification' in Windows. Could you please elaborate a bit?

I do not know - I never use this setting. My screens at home are 27" with 2560×1440 points and on the road I use a MS Surface 12" with 2736×1824 - and in any case Windows is set to 100%. When I do trainings, I rescale sometimes to 150% or 175%, but never have encountered what you show.
So try to use View -> Reset window layout. I have too look later, where further view settings for Studio are stored, but have to take care about different things now.

BTW, Windows looks perfect with 100% and not good with 150%, it is all too huge then...

Hi Stepan,

Have you tried this app?

https://appstore.sdl.com/language/app/change-scaling-behaviour/790/ 

I used 'Reset window layout' million times. I've just got used to this issue since 2019 was released 2 years ago, but recently just recalled that I can ask about it here. Weirdly, this idea did not come to my mind before. I mean the issue is as old as Studio 2019 for me, even though I ask as late as today. 
My 3 monitors are big enough (24") too, but icons and captions and menus etc are extremely small. I know that I can choose from small icons, medium icons, and big icons, but it only applies to the desktop icons. Even the desktop icon captions remain small.
I think Windows 10 somehow causes this. I can't remember that I experienced the same with Win7.

Hi Nora,
Not yet. Will try it right now. Thank you

This "issue" is very strange, as I have seen Studio on so many PCs and never ever seen something nearly similar. Does the window not maintain its size after being resized?
Usually this window is far too small for my needs, never that big as you show.

Exactly! And even if I adjust it manually, it only shrinks to a certain size, which is still too big. And no, it does not keep its size after shrinking.

OK, please go to File -> Setup -> User profiles, backup your current user profile (export). Then load a profile from the Studio installation folder (c:\program files...) and check again.

The only effect from the app was that it prevented my alternative CAT tool from launching with an error message saying something about wrong syntax in manifest.xml file and SideBySide issues (have no idea what sort of error it is).
After several hours of watching youtube and reading articles, I gave up and was about to reinstall my Windows. As a last resort, I decided to visit that magic app again [to say goodbye] and noticed that its Apply button changed to Undo. I pressed Undo. This removed the SideBySide  error and recovered my alternative CAT tool after reboot. Thank god. Now I came to status quo as before my vain efforts.
Just now I found this thread. Matthew Docherty described a similar, if not same, issue. Unfortunately, I did not find his question before I posted mine... It could save me time.
Nevertheless, thank you Jerzy and Nora for your input.

Jerzy Czopik said:

BTW, Windows looks perfect with 100% and not good with 150%, it is all too huge then...

Compare this. With my normal vision (I don't wear glasses or lens), I can hardly read time and date in the right bottom corner. No, 100% scaling is not acceptable for me.

Well, I wear glasses and prefer 100%, certainly. A screenshot does not represent exactly what you see, but even with the very high resolution of MS Surface 100% is better. You can simply bring more necessary information on the screen in these parts of programs, which are really important. In Studio for example, this is the editor, terminology recognition, translation results, error messages and termbase viewer. With a bigger scaling I would not be able to place all this on a single screen, but when using 100% I have this and can still work comfortable, as the text shown in Studio is big enough. Menus, however, are fully unimportant - I don't need to read their descriptions, as what I use is well placed with big symbols or can be accessed with shortcuts.

Well, I wear glasses and prefer 100%, certainly. A screenshot does not represent exactly what you see, but even with the very high resolution of MS Surface 100% is better. You can simply bring more necessary information on the screen in these parts of programs, which are really important. In Studio for example, this is the editor, terminology recognition, translation results, error messages and termbase viewer. With a bigger scaling I would not be able to place all this on a single screen, but when using 100% I have this and can still work comfortable, as the text shown in Studio is big enough. Menus, however, are fully unimportant - I don't need to read their descriptions, as what I use is well placed with big symbols or can be accessed with shortcuts.