Hi,
Thank you for posting your question here!
This happens because the Renew button in Minecraft opens a Microsoft Store overlay that fails to load so to fix it first sign out of the Microsoft Store and Xbox app then restart the device sign back into the Microsoft Store and confirm the correct account is logged in. After that, open Minecraft and try renewing again. If the window still stays blank, go to account.microsoft.com/services find Minecraft Realms and renew it directly from there instead of in game. If that still does not work, cancel the expired Realm from the Services page and create a new Realm in Minecraft which clears the stuck subscription state on the backend.
Let me know if you need further assistance, feel free to ask me by clicking "Add Comment" or "Add Answer" if you cannot add comment so your response will be visible. Thank you and I appreciate your effort.
Regards,
Angelique P.