Hi @frob
Per my research, there is no obvious difference in co-authoring between SharePoint Online and OneDrive.
You could refer to the two articles for more information:
https://support.microsoft.com/en-us/office/work-together-on-office-documents-ea3807bc-2b73-406f-a8c9-a493de18258b
https://www.sharepointdiary.com/2018/09/co-authoring-feature-in-sharepoint-online.html
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