Hi,
Outlook for Android shows multiple accounts only if each one is fully authenticated and has email sync enabled. If the accounts appear under “Accounts” but don’t display messages, it means they were added but not syncing.
What I suggest is:
Go to Settings → Accounts → [each account] → ensure Sync email is ON.
Remove and re-add accounts using full sign-in (not alias linking).
Check filters (set to All mail) and update the app.
Happy to help!