If it's very thick and on a shower door the quickest and easiest way to get rid of it is to put a straight razor blade in a holder and scrap it off. Work very gently. I've done this on bathtub tile while the tub is dry. The scum falls in the tub and get it out with the vacuum cleaner attachment. I quit using bar soap for this reason. Liquid cost more but it doesn't form soap scum.
Where is this soap scum? If it is on dishes from a dishwasher, you likely need something like vinegar to remove it, as it is deposit from detergent. If it is on shower doors, something like Mr. Clean and Magic Eraser will likely do the trick.
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