Can confirm, this occurs even on Ventura (latest version). Wiping all cached data related outlook.live.com temporarily resolves the issue, but only for the first page load. Closing the browser/tab and visiting outlook.ive.com again immediately results in the same issue (i.e. very long loading times), I'm curious as to whether this is caused by some specific API used by the website. If there's something I can do to aid in debugging, please let me know!
Note: The issue occurs only when logged in. I've had my session expire before, after which I went through the login flow without any issues, thinking that perhaps the loading issues would be solved as well, only to encounter the issue again when actually loading outlook.live.com while authenticated.