I am afraid your question is a little confusing and lacking information that we'd need in order to be able to help you.
The confusing part is "board type list" - Sprint and Kanban are types of board, but Next-gen (now team-managed) is a project type (which could also be Sprint or Kanban, and generate a board of the right type when you create the project that way).
I mean - I do not understand what you are looking at when you are looking at the "board type list"
Secondly, the missing information (which will probably help us understand the confusing part) - where exactly are you seeing this field? Maybe you could give us a screenshot and include the full url?
Bear in mind we're a community of people talking about Atlassian, we are not Atlassian themselves (although there are many of them here) and we have no access to your systems.
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