Question: Can I use a Joker as a single tile or in a pair?

Answer: Under no circumstance can a Joker be used in place of a single tile or a pair. If you were to call and expose a single grouping or a pair with a joker, your hand would be declared dead.

Examples of Single Tiles are NEWS, year hand groupings such as 2024, individual tiles such as 123 or 46, and all hands under the Singles and Pairs Section.
Examples of Pairs are, FF, 22, DD

Source:  Mah Jongg Made Easy 2024 pg. 24, #9