Unfortunately, @Alan McBees answer is wrong, the list is refering to App Services (Microsoft.Web/sites) and not App Service Plans (Microsoft.Web/serverfarms), and also is not complete (see linked question, not the accepted answer).
The kind property for the App Service Plan has no meaning.
Note that the kind property also shows up in App Service Plans (ASP). At this time, the value of this property for the ASP is meaningless and has no impact on your resource. For example, you can set kind to “Linux” for the ASP, but that won’t make your ASP a Linux ASP; the reserved property is what makes this distinction (if reserved = true, it’s a Linux ASP, otherwise it’s a Windows ASP).
See 2nd to last paragraph here:
https://azure.github.io/AppService/2021/08/31/Kind-property-overview.html