Hi David,
So from what I gather, it’s actually the opposite. Microsoft changed to supporting query strings within redirect URIs for Active Directory in July 2019 (as documented here: https://docs.microsoft.com/en-us/azure/active-directory/develop/reference-breaking-changes#redirect-uris-can-now-contain-query-string-parameters). However, it appears some aspects of the Application Registration UX have not been updated to recognise this change.
Personally I’ve found that this limitation only occurs when trying to register a personal Microsoft Account (i.e. not a paid for business office 365 account – incidentally personal accounts can’t use the Graph Mail API anyway). The limitation also seems to kick in if you select any of the multitenant/personal account options under supported accounts (shown in Step three of my setup guide).
So long as you’re registering a paid for business account, and have only selected the single tenant option under the supported account options, I’ve found you don’t get any issue with the query string redirect URI (and 300+ others would tend to agree based on the plugin active installation count to date). That’s not to say that some individuals may not find that Azure throws an error, although the link above suggest you can still force Azure to use the redirect URI by editing the application manifest in the Azure portal.