Display scaling and resolution

That's normal.

Macs don't handle high-PPI displays in the same way that Window PCs do. They use a Retina scaling system where in a Retina mode, the drawing canvas can have twice as many pixels in each direction as the nominal "resolution" in Displays {Preferences/Settings}.

The way that you set text and object size is by setting a Displays {Settings/Preferences} "resolution". When this is a Retina mode, the actual drawing resolution will be greater.

E.g., on a 27" 5K Studio Display,

• You might choose Retina "2560x1440" mode in Displays Settings.
• The drawing canvas would then contain (2x2560)x(2x1440) or 5120x2880 pixels.
• macOS would use the high resolution of the drawing canvas to draw letter shapes more precisely. Retina-aware applications (just about all of them, these days) could fill in photo areas using the high resolution of the canvas. The system would be using the full resolution of the 5K display – just using it to draw things in detail, rather than to cram more and more, tinier and tinier, stuff onto the screen.

I believe one of the reasons Apple did things this way was for backwards compatibility. In the early days of high-PPI displays, I think a lot of Windows applications simply ignored the global scaling factor, and as a result they displayed unusably small output on high-PPI displays. On the Mac, the way the APIs were set up gave the system a chance to identify which drawing calls were from legacy applications, so the OS could transparently adjust those calls to make things work better.

Did you have a question?

Well, I don't know what the problem is. So if you could explain.