Explanation
Page layout and field level security are two factors that determine whether a user can see a new field on a record. To troubleshoot this issue, the administrator should ensure that the page layout for the user's profile has been updated to include the new field and that the field level security of the field for the user profile allows read or edit access. References:
https://help.salesforce.com/s/articleView?id=sf.customize_layoutoverview.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.admin_fls.htm&type=5