I'm a little confused with the question? There is no maximum number of dashboards that can be created (the maximum number that can be stored on Tableau Server depends on it's capacity but there is unlikely to be an issue), the only limitation is how fast you (or your team) can create them.
If this solves your issue please mark the answer as correct, if not let me know!
That's like asking someone how many steps can be taken in a month. Steps are completely dependent on the person and living conditions. With dashboard creation, it's completely dependent on the data, the requirements for the dashboard, and of course the complexity.
I can create 10 very simple dashboards in a single day but they may not be as valuable for my clients as one dashboard that takes me a week to create.
If your boss, or a client is asking you this, you need to understand what they actually want you to create.