Setting connection string with username and password in ASP.Core MVC

Can you try User ID instead of userid?

Note the main difference is in the space between user and id, the case doesn't matter

That's because the correct keyword is User Id, as shown in the following example:

"ConnectionStrings": {
    "DefaultConnection": "Server=myServerAddress;Database=myDataBase;User Id=myUsername;password=myPassword;Trusted_Connection=False;MultipleActiveResultSets=true;"
  }

user<space>id

Server=myServerAddress;Database=myDataBase;User Id=myUsername; Password=myPassword;

https://www.connectionstrings.com/sql-server/