Per Microsoft Engineer (11/17/23):
"We've had a few people reach out regarding the New Outlook experience, mostly about changes and items missing.
Currently it's in an early release stage, so it's missing a good bit of the functionality of the Outlook we've been used to for quite some time.As yourself and the forum posts have mentioned, there is currently no File tab. Other important features such as the ability to import/export .pst files for mail and contacts is missing, and you can't have double spaced emails for viewing, just as some examples.Microsoft will be implementing features back into the new Outlook that were not ready for it's initial release, this is more like a trial run to gauge feedback on the new UI and layout, which is much more akin to Outlook on the web. Outlook on Mac has been going through a similar release for the past year or so with features being added gradually before finalization.For the time being, if you need to access missing features, such as import/export, we recommend using the Classic Outlook experience until the new version is more fleshed out and finalized. There's no ETA on the rollout for the finished product, but the classic Outlook will continue to be useable for the foreseeable future."