When searching, remember, a few words are better than many
ID48-Joker Exchanges Are Optional
Question: The other day, I strategically did not do a Joker exchange. Another player made a big deal out of it as if I’d made a mistake. Is there a rule that requires me to do a Joker exchange?
Answer: There is no requirement to do a Joker exchange. In some cases, a player may choose not to do a Joker exchange if they want to prevent another player from being jokerless. If they are going for a jokerless hand, doing a Joker exchange and then discarding the Joker would provide valuable information to the other players. However, if there is still a symbol tile available to someone else, it might be wise to consider taking the Joker to prevent another player from getting it.
Source: Mah Jongg Made Easy 2020 page 22 #3