Enable Global Advanced Logging
https://support.microsoft.com/en-us/topic/how-to-enable-global-and-advanced-logging-for-microsoft-outlook-15c74560-2aaa-befd-c256-7c8823b1aefa
File -> Options -> Advanced
[/] Enable troubleshooting logging (requires restarting Outlook)
Click OK.
Exit Outlook
Start Outlook.
Attempt to add your POP account.
Exit Outlook.
Open %temp%\Outlook Logging
Look for a file named after the POP account with today's date. e.g.
XXXXXgmailcom-Incoming-02_22_2026-01_17_19_424.log
You should see some details that might give you a clue.
Turn off Logging.