Hi @Nick J. Knodel
Welcome to our forum!
Yes, it is possible to add a personal calendar. As stated in the documentation, you can connect a Outlook.com or Google account to your work or school account. However, only add it to Outlook on the web. Please check if your account type is outlook.com or Google account.
If that doesn't work, try deleting the account and adding it again. And contact your IT admin to make sure your work account has the permissions you need to add a personal calendar.
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