This was an InfoPath form library form.
What we found out is that When we go to File -> Form Options (Advanced form options) and then click on “Show InfoPath commands in Ribbon or toolbar” under “Web Browser” category as shown in the fig below:
Read some SharePoint InfoPath tutorials:
- Make attachment field mandatory in InfoPath Designer 2013 in SharePoint Online list
- InfoPath 2013 show hide section using Rules in SharePoint online
- Limit attachment size in InfoPath 2013 SharePoint online
- How to publish an InfoPath form to an email in SharePoint 2013?
- How to publish InfoPath forms as a content type in SharePoint 2013?
Hope this will be helpful.
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