The vast majority of upgrades to Dynamics 365 Business Central are completed. If you are on a tenant that has not been upgraded yet it is because you have a V1 Extension installed that the developer has not provided an update for. We cannot upgrade these tenants unless we either A: Uninstall the Extension. B: Receive a V2 update from the developer of the extension.
If you would like to be upgraded to Dynamics 365 Business Central please engage your CSP Partner to open a case with the support team. We can advise you on which extension is preventing the upgrade and you can decide if you'd like to uninstall it or not.