Model Y owners who have taken their Tesla through a touchless car wash report that the process leaves a brown stain or sometimes a rainbow pattern on the blackout trim parts; perhaps you have not had the issue. The stain is supposedly caused by the high pH detergents used in the touchless wash and can be easy or difficult to remove, based on reports.
I have had this problem. Even using a reliable car wash that we have previously used on our Model X, and previously a Model 3 and S. It’s pretty disappointing to not be able to get it looking just right yet. Hoping to get it restored to it’s original look ASAP.