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Dear Dev0p,
Good day! Thank you for posting to Microsoft Community. We are happy to help you
Based on your description, we understand that you want users to be able to access SharePoint through Access, and that you have purchased a subscription to SharePoint.
Business accounts are typically created in the Administrator Center, Add users and assign licenses in Microsoft 365 - Microsoft 365 admin | Microsoft Learn
In your case, I don't think you need to create additional accounts, if the user has an account themselves, you can invite the user directly and thus assign them access to SharePoint. Ref:Share a list or list item - Microsoft Support
We look forward to your reply. Thanks for your cooperation.
Sincerely,
Tin | Microsoft Community Moderator