From this article, we can find the reason we can't see Allow sites to be reloaded in Internet Explorer:
If you are on a device managed by your organization you will NOT see the option to Allow sites to be reloaded in Internet Explorer under edge://settings/defaultbrowser to allow Internet Explorer mode through the More tools menu.
In this situation, you can set your site to be opened in IE mode by configuring IE mode policies. For the detailed steps, you can refer to this doc.
There're two steps required to configure IE mode:
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Regards,
Yu Zhou