Using older versions of Outlook for Mac for personal email and calendar
Corentin, you may want to actually check the product before making those conclusions. As I mentioned in my message, until the recent update, I had been able to do this for months with this account.
I have contacted the support team within Outlook. For anyone else facing this issue, turns out they are aware of the issue a fix should be on the way.
I've used the product for quite some time… I've been an MVP for Office for Mac since 2002. I'm not a paid contractor doing this on the sideline and I did check Outlook.
You'll see that there are other threads mentioning the same issues on the forum.
Up until recently, Outlook used to connect through IMAP and you were then just fine moving emails around in folders. A somewhat recent change brought OAuth support as well as calendar and contact syncing (requires a license through subscription or a perpetual license for Office 2019, not 2016). Since then, users have been enable to rename the Gmail folder, or move emails to the folders.
Microsoft is indeed aware of the limitation and they are indeed very likely to be working on implementing a better support for the folders for Gmail and Gmail-based accounts. You'll notice that this is also what's implied in Alan's reply to your original post.
Corentin