Same here. Have Xbox Game Pass and it appears inactive in Battle.Net. Answer from the support guys:
"We understand your concern regarding the inactive status that appears on Battle.net, despite having Xbox Game Pass as shown in your screenshot. We’ve received similar feedback about this issue, and in this case it appears to be related to Game Pass and Xbox.
On our side, everything seems to be in order. We recommend contacting Xbox Game Pass support for more information or to resolve any potential issues with a bug or your subscription. You can do it through the following link:
https //support xbox com/"