How to add read option in Manage Access for page in SharePoint Online?

Hi @Zhang, Eric 

Thank you for posting your question in the Microsoft Q&A forum.   

Regarding your issue, the Share or Manage Access panel in SharePoint often defaults to simplified sharing options. If the library or site permissions are configured in a way that doesn’t expose the Read permission level through this panel, you’ll only see "Can edit". 

Here are a few steps you can try: 

Use Advanced Permissions:  

• Instead of using the "Share" use the Manage access > Advanced permissions. 
• 

• Select site Visitors or Members > New (add users to this group)  
• 
• On the Shared with choose Advanced 
• 
• Click on Grant Permissions and enter the email addresses 
• 
• Click Show Options and choose Read from the permission level dropdown. 

Note: Make sure the group you're sharing with also has the Read permission level defined in the site settings. 

For more details, please refer to: Customize permissions for a SharePoint list or library

Hopefully it will help work with your issue and if it doesn't feel free to comment below to let me know so I can assist you further. 

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