Hello @Christopher Andrews , using microsoft graph, you can create pages through the following APIs, which support adding HTML files to your pages.
POST /me/onenote/sections/{id}/pages
POST /users/{id | userPrincipalName}/onenote/sections/{id}/pages
POST /groups/{id}/onenote/sections/{id}/pages
POST /sites/{id}/onenote/sections/{id}/pages
Here is the documentation for your reference: https://video2.skills-academy.com/en-us/graph/api/section-post-pages?view=graph-rest-1.0
Hope this helps you.
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