Color calibrated workflow?

Hello all,

first of all: I know there are many discussions about color calibration - however, I don't understand one point, so I hope you can help me.

I am currently using a Mac Studio with two monitors - one of which shows a clean video feed from Resolve. I have calibrated this monitor to Rec709 using a Calibrite Color Checker Studio - so under the "Display" settings in macOS I can switch between "some" setting and the calibrated setting, which leads to a visible color change on the monitor

On many websites it is now mentioned that a really color calibrated process is only possible with e.g. an "Ultrastudio Monitor" or similar - with the reasoning that the "operating system changes the colors and no good signal path is given anymore".

From my point of view there are two possibilities:
1) The signal is send via Thunderbolt to an Ultrastudio, which then gives it "as is" to the monitor. Now it depends on the monitor that it is calibrated - e.g. via an interconnected LUT box or an internal hardware calibration.
2) The signal goes via the computers graphics card to the monitor. A calibration has been done via the Color Checker Studio, so the "correct" colors should be shown on the monitor?

So why do you need an Ultrastudio - isn't the point of a color calibration process (on the Operating System level) to ensure that the colors are displayed unaltered?

Thank you very much in advance, best
Christian