Unable to find people button on the pane

Hi Tony Nuo Wang,

Thank you for posting in the in the Microsoft community. We are happy to assist.

Based on the information you have shared with us; I understand you have a concern regarding the people tab button that has disappeared in outlook. To fully understand the scenario, I would like to ask some questions to narrow down the situation work toward the resolution.

May I know if the people tap button is visible in the outlook on the web(webmail)?

unfortunately, the screenshot you have share with us was not successfully uploaded, could you try the shared the screenshot again? You can try to share it in the private chat if it contains any sensitive data.

May I confirm if the affected account has an Office 365 subscription. Are you using Microsoft 365 Business Basic, Standard, Enterprise, or Education? Alternatively, is it Microsoft 365 Family, Personal, Office 365 Home and Business, Office 365 Home, and Student, or a Personal (Outlook.com, Live.com, Hotmail.com) subscription or any third-party account?

May I know if this issue happens in a particular client application like new outlook for windows, classic outlook, outlook for mac, or outlook on the web (OWA)

Please may I know if the account is configured in the outlook using POP, IMAP or MAPI outlook profile,

You can check this in the outlook by clicking on File>>info

Please shared with us the screenshot of Account information section (please hide the emails address)

Please note that my initial response may not address your current situation immediately. However, with your help and more detailed information, we can work together to find a direction specific to your current situation.

Note: To protect sensitive information, please share with use the above   requested screenshot information in "View Private messages".

Here are the steps to open "View private messages":

To view private messaging options> Sign in to Microsoft Community, use the email account where you posted this thread information to Microsoft Community, > click your profile picture in the top right, > select the My Profile option.

I look forward to your next update on this in private message. Thank you so much for your precious time. stay safe and healthy.

Click the square icon at the bottom if the left bar -Right click on People and pin it.