MVP is a Minimum Viable Product created in the initial phase of business with minimal features that demonstrate that would demonstrate your business idea. It is usually developed to validate your assumptions about usability of product.
Beta is a form of acceptance testing where the version of product given to end users to test is almost the final product. Beta testing is also a phase of data collection from users for future improvements to be made in the product.
MVP phase is pre final product and Beta phase is when the final version of product is almost ready and is being given to end users for feedback.
Please find this article for more help on the topic: https://www.feedough.com/mvp-vs-beta-difference/