Using New Outlook on Windows for personal email, calendar, and contact management
Hi, let me help you.
Click on that account's name in the left pane, then look for the three-dot menu (or right-click the account name) and choose "Manage folders" or "Pin folders." That'll open the full list of folders tied to that account. Scroll through it and see if Inbox shows up there with an unchecked box or an unpinned icon.
Let me know what that list looks like — whether Inbox is in there just unchecked, or missing from the list entirely.