Hm, another user has encountered seemingly the same problem today in How to setup (Admin) user at the first start for self-hosted version? - #5 by nigel .
Could you provide more details on how exactly you are running Baserow including:
- The commands you’ve used to start Baserow showing your env variables if set
- The docker version if known
- Your operating system / version
- Are you accessing Baserow remotely from another machine? If so have you set the BASEROW_PUBLIC_URL environment variable to be the URL in your Browser that you are using access Baserow remotely?