A user can only select one object at a time. However, they can select multiple fields of the selected object and provide field level security(FLS).
Steps to select multiple fields to provide Field-Level-Security.
- Go to Mass Assign Permissions App
- Click on Mass Assign Field Permissions Tab.
- Select object > Select Profile > Select field (here, you can select multiple fields)
- Click on fetch Field Permissions button.
- It will fetch the table having all selected fields.