MacBook Pro function keys
I believe you are misunderstanding the information you read.

On older MacBook Pros, the top row of function keys double as system settings keys just as they do on PCs, but with one important difference:  On a PC, the top row keys act as function keys primarily, and you use the Fn key to use the secondary setting. Macs default to the exact opposite of this. The top row of keys act as settings keys primarily, and you use the Fn to use them as regular function keys. This can be confusing to newcomers at first.

This also adds ambiguity into the documentation you found. It says that F1/F2 adjust the screen brightness, but F1 and F2 don't actually do anything. The screen brightness controls are just ON the F1/F2 keys.  The documentation knows that the primary and secondary functionality of the function keys is reversed on Macs, so that's why it said to use just F1/F2.

Lastly, I said in my first paragraph that older MacBook pros act this way. Newer MacBook Pros with the Touch Bar do not have a row of function keys. The Touch Bar always displays whatever function will happen when you touch it. When you press the Fn key, it shows the function keys because that's how older models would behave.

Just remember, you're not actually after the F-keys. You're after the functions that used to be on those keys when there was an actual row of function keys instead of a touch bar.

Make sense?