Hi AbernathyB,
Sorry for the inconvenience caused. From your description, it seems that all of your Office applications are missing a command in Office Ribbon. May I confirm with you whether the “Insert Icon” command you are referring to is
“Icons” command as the screenshot below?

If so, generally, you can find this command under Insert Tab> Illustrations> Shapes> Insert Icons, which this option should come along with Insert tab as long as you enable “Insert” Tab in Option > Custom Ribbon

If not, please share more details about “Insert Icons” you are referring to at your convenience. Thank you.
At meantime, may I know the following information at your convenience?
1: The version of Office application. You can go to File > Account> Under Product Information to find details.
2: Do all the users in your organization missing this “Insert Icon” option in Ribbon?
Best regards,
Dihao