Screen resolution / scale on MacBook Pro with Retina screen

[#1]

For example, if I open a photo with the dimensions 800 px x 800 px in PS, I would like it to be displayed in the appropriate size when I go to 100% view. So the size that it will later have on a website or when it is printed.

My current mass:

287mm width of the monitor: 25.2 = 11.29 inch width of the monitor
2560px screen resolution (retina): 11.29 = 226.74 PPI

I entered this value in the preferences under "Units of measurement and rulers" under "Screen resolution".

Would that be correct so far? 

Screenshot: https://www.dropbox.com/s/qbo0dqk5en5yh1i/Bildschirmfoto%202021-01-10%20um%2016.19.26.png?dl=0

[#2]

For example, if I open a photo with the dimensions 800 px x 800 px in PS, I would like it to be displayed in the appropriate size when I go to 100% view. So the size that it will later have on a website or when it is printed.

My current mass:

287mm width of the monitor: 25.2 = 11.29 inch width of the monitor
2560px screen resolution (retina): 11.29 = 226.74 PPI

I entered this value in the preferences under "Units of measurement and rulers" under "Screen resolution".

Would that be correct so far? 

Screenshot: https://www.dropbox.com/s/qbo0dqk5en5yh1i/Bildschirmfoto%202021-01-10%20um%2016.19.26.png?dl=0

[#3]

100% has never meant "life size" and cannot be adjusted. It means "one screen pixel per image pixel". To view it at a particular size, just do the math to work out what zoom is needed. For web site use, 200% is what you need. 

[#4]

All right. Thanks. I was just confused why this was the case with CS 6 and now no longer ...

[#5]

CS6 wasn't able to make proper use of the new retina screens - you weren't getting what you paid for. But Adobe caught up with the tech so we can take full advantage of these screens - which are probably more important to photographers than anyone.

It's a common feeling that 100% means something special, and to pick one app (which does what we want) as "right" then try to fix the others. Really we have to go with the flow, and use zooming as a routine.