From Nielson Norman Group: https://www.nngroup.com/articles/everyone-as-users/
Summary: Even if your target demographics are very broad, you should still identify specific groups of users within that audience to use for UX research and design.
When a design serves a large and varied population of users, stakeholders sometimes direct that the design must target “everyone.” This approach may feel more inclusive than focusing on certain categories of people, and is especially attractive for organizations that have a strong need to attract more customers or users.
But avoiding any definitions of the target audience actually leads to a less usable experience for most people. Without an understanding of who the users are, you risk getting biased research findings and incoherent design choices.
You don’t always need precise categories of user characteristics, but you do need some idea of who will be using the design, and what they’ll try to do with it.