Microsoft
Microsoft
Microsoftrallenh - Regarding Thunderbird supporting OAuth2, you should officially check with the Thunderbird team, however from a few quick tests yes they do support OAuth2.
MikeB74 - Full PST support is coming and being built as mentioned on the Outlook Roadmap. At this Point the Initial versio of PST support in new Outlook for Windows has hit General Availability which gives you the ability to read/search mail items in the PST. Microsoft 365 Roadmap | Microsoft 365
compsearcy - App Passwords will also be disabled for Outlook.com accounts, leaving any form of basic auth does indeed leave vectors open for password spray attacks.
eltonline and PaulFinnEdison - Regarding the Gmail App Sync, I believe they have chosen to setup Outlook.com via imap in their configuration/setup experience. As you know IMAP only supports syncing mail items, it does not support Calendar and Contacts. If Google wanted to support those other item types, they would need to build support and leverage something like EAS, or other APIs that also support Modern Auth against Outlook.com. I recommend contacting Google to request further support of your account. As always there are also free Outlook clients that will fully support syncing all of your content.