The only way to know is to experiment.
Whack everything to max settings, get into the plane you fly the most and note the performance.
If the system is struggling begin whacking down sliders.
For example I cannot tell the difference between Ultra and High when it comes to buildings and vegetation so I keep it at high.
Different gamers want different things. If much of your time is spent at 37,000 feet then you might not be fussed about trees, grass and bushes at Ultra.
Thats just one example.
This is a very subjective thing and while the videos point you the right way it is your eyes and brain that will deliver the verdict for your preferred settings.
Have fun and it doesn’t take too long to find the sweet spot for a system. Initially you’ll be constantly going in and out of the menu. As things settle in you’ll be doing that less and finally when everything humming along you can focus on the flying.
Just ensure you are in the same plane at the same airport with the same weather conditions as you play with the sliders.