Limit a single users FTP access on IIS10 to a IP address
Solution 1:
You don't have much flexibility when using the default IIS providers and settings.
Instead, to achieve the level of control you wanted, you have to write your own authentication provider with IP checks, and Microsoft has an article with a similar case,
https://docs.microsoft.com/en-us/iis/develop/developing-for-ftp/how-to-use-managed-code-c-to-create-an-ftp-authentication-provider-with-dynamic-ip-restrictions