Ansel Adams chose ISO first.
Your pictures suck compared to his.
If you are learning, or relearning, manual exposure I will tell you there is a progression of choosing the 3 elements of exposure that works every time. The 3 elements are ISO, aperture and shutter speed, in that order, at least at first.
In the 1920s Ansel Adams began taking some pretty good pictures. He knew all the rules about photography. He knew all the numbers and formulas and even created some rules of his own that we still use. Guess what? Adams had to deal with ISO too and he didn’t have a camera that would do it for him.
We are spoiled and it complicates ISO. When did Adams choose his ISO? Before his trip, right? Days, weeks or months before setting his camera up for a shot.
Our fancy schmancy digital cameras have auto ISO. When we walk out into the sunlight the camera chooses 100, in dark settings it chooses 1600. Why are we always crying about ISO and noise?