Currently, there is a limit on the amount of queues you can have in a JSM project of 200. If you try to create a new one above that limit, the "Add queue" button is greyed out and if you hover over it, a tooltip appears saying: "You've been busy! Your project has reached the limit of 200 queues. You'll need to delete a queue before you create a new one."

It would be nice for this limit to be increased for those with intentionally large and complex projects.

A suggestion for those with such large projects in the mean time; consider deleting unused queues, or splitting your project up into several smaller projects where each project can use a smaller amount of queues.