Hi, Pfp_855.
I'm Jen, I'm also an Outlook user just like you. I'm not working for Microsoft but I'd be happy to help you figure this out.
If you mean alias added to your account, you can check them by signing in to https://account.microsoft.com/account > click on Your info tab then under Account info click on the Edit account info link > from there the Account Alias are listed.
However, if you're referring to a connected account, this feature has already been discontinued since May 10 2021 but if you have a connected account prior to this date, it should still appear in your settings. To check this, click on Settings > View all Outlook settings > Sync email > Manage your connected accounts.
You may also want to check the Rules tab if there's any rule created to forward emails or the Forwarding tab to check if it's enabled.
I hope this somehow helps. Feel free to share how it went.
Kind regards.