@heidigfx
I'll try to explain:
fact: The digital photography size is the number of pixels that we express in "Wide x High". You can express this in Inches, cm, pixels, etc.
Example: 10 MP photo has 10036224 pixels, which is the result of multiplying 3872 pixels Wide x 2592 pixels High. (this numbers can vary slightly from different manufacturers)
ppi is the number of pixels per inch a screen has.
dpi is the number of dots that a printer put in an inch of paper.
ppi and dpi are used indistinctively normally. Is a common error. You have hundreds of pages talking about this.
When you set your photo to 72ppi, 300ppi, 10000ppi or 1ppi you don't change the size of the photo (at least that you resize). The thing is you can set your photo to whatever number of ppi without changing the size of the photo or any other thing. The photo is exactly the same.
What you just did is changing the metadata which orders the printer how to print the photo, how many dots per inch has to put on the paper. For that, they should express this in dpi instead of ppi
So you can forget about all this and focus on the real size. For screen show is completely useless and setting to 72 or 96 or whatever is completely useless. If you know you are going to print at 300, for example, stack to that setting just in case you forget to change it latter and waste a paper
There's a lot of pages talking about this. For an explanation about where this 72 number came up for example:
https://www.photoshopessentials.com/essentials/the-72-ppi-web-resolution-myth/