You can refer to this article about how to use IE mode.
Only those sites that you specifically configure (via policy) will use IE mode, all other sites will be rendered as modern web sites. For a site to use IE mode, you need to:
- List the site in the Enterprise Mode Site List XML defined in one of these policies:
- Microsoft Edge 78 or later, "Configure the Enterprise Mode Site List"
- Internet Explorer, "Use the Enterprise Mode IE website list"
- All Intranet sites when the Send all intranet sites to Internet Explorer group policy is enabled (Microsoft Edge 77 or later.)
So you need to check if you have added the site InfoPath 2010 in the Enterprise Mode Site List and configured IE mode policies correctly. For the detailed steps about configuring sites on the Enterprise Mode Site List and configuring IE mode policies, you can refer to this article and this article.
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Regards,
Yu Zhou