The tooltip for the "Use DIA precursor window for exclusion" says:

If checked, the precursor exclusion window is taken from the Full-Scan settings instead of being symmetric around the precursor m/z. This is recommended for DIA/SWATH data.

Skyline only allows you to check the checkbox if your MS2 full scan acquisition method is "DIA" and you have prespecified the isolation windows and your isolation scheme has specified the window width (i.e. you did not choose "Results Only").

If your acquisition method is not DIA, then Skyline does not show you the "Use DIA precursor window" checkbox. Instead, Skyline shows you a textbox called "Precursor m/z exclusion window" where you are supposed to type in a number.

The tooltip for the "Precursor m/z exclusion window" textbox is:

A m/z window around the precursor m/z within which transitions are excluded, or blank. A window of 20 will exclude all transitions within 10 on either side of the precursor m/z.

So, the "instead of being symmetric" part of the first tooltip isn't saying that the checkbox toggles between symmetric and asymmetric. It's trying to make a distinction between the behavior that the checkbox is offering, versus what would happen if you typed a number into the textbox. This is a little confusing since there has never been a case where Skyline would be showing checkbox and the textbox at the same time.
-- Nick

Thank you very much for the explanation, now it makes sense.

With best wishes,
tobi