Hi @Anonymous ,
We have Microsoft Graph API to get SharePoint Online site storage report using this getSharePointSiteUsageStorage API but currently there is no API avaialble to set or modify SharePoint Online Site storage quota. Since this feature/functionality is presently not avaiable, you can submit a feature request idea using this support link, which will be monitored by Microsoft team and make the enhancements to Microsoft Graph APIs. I will also upvote for you.
Hope this helps.
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