As long as you have the font installed on the local machine and have given permissions to the web app to access local files, you should be able to use it. In Word Online that is, all the other apps have limited selection of fonts available.
How to add font in Office 365 when I use on web

How to add font in Office 365 when I use on web
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Emily Hua-MSFT 23,781 Reputation points Microsoft Vendor
2022-09-02T09:18:22.493+00:00 Welcome to Q&A forum ~
Please check whether michev's reply is helpful.
Here is an article you can have a look : Add a font.Besides, if you have further issues on Office for web, it's recommended to post a new thread on Microsoft Answers Community. As Office for the web is not supported on Q&A forum at current time.
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