This is a known issue (tracked at https://bugzilla.mozilla.org/show_bug.cgi?id=2007074, as mentioned by a previous comment). A fix has landed in Thunderbird Daily a couple of weeks ago, and should be released in Thunderbird 154 which comes out next month.
> At present, EWS is our best way to enable support for both Exchange Online and on-premise installations.
> Graph API has been considered and may be considered again in future, but it currently provides narrower support than EWS and lacks some functionality for desktop applications. Even with the announcement that EWS support will be removed for Exchange Online, it's still valuable in the short term for enabling access for a wide userbase and in the long term for supporting users using on-premise installations.