Hi @Williams, Kim (US) ,
Are you using modern experience or classic experience?
In classic experience you could add Content Editor web part to list page. Content Editor web part allows authors to enter rich text content.
Edit page > Add a Web Part > Media and Content > Content Editor
My test result:
But per my research, it is not possible to add a description text in the list page if you are using modern experience. Classic list experience can be a workaround.
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