Hi @sjamesworld - if you search the forums, there are several topics around this same question (for instance, here and here). Generally speaking, there is no maximum, but you will start to run into performance issues the more rules you add.
It’s important to remember that DMN is meant to be maintainable by humans, and a table with that many rules may be hard to maintain. Could you separate it into smaller tables and chain them together perhaps? I would also recommend reading through those previous threads and searching the forum for other topics and experimenting with the suggestions there.