I've fitted '21 cables to '18 before without trouble so I dont think they are different in lenth.

However a Honda cable isn't red so it could just be a poor copy of a stock one.

If you have a dry clutch there is a easy away around it though. You can fit F3/RS clutch shims to the push rod top hat to reduce free play but making the push rod longer. HRC make a number of different sizes for such a thing.
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If I have to take the carbs off once more...