Hi Georgie,
Sorry for the inconvenience it may have caused.
Actually, SharePoint document libraries can be shared with external users.
In a Microsoft 365 organization, SharePoint external sharing is affected by many factors such as Azure Organizational relationships settings, Microsoft 365 Groups guest settings, SharePoint organization level sharing settings, SharePoint site level sharing settings, etc. Only after these settings are set to allow external sharing, a specific site or files/folders in the site can be shared to external users. For more information about it, see Collaborate with guests in a site.
And there’re some other knowledge-based articles for your reference:
And to share a specific document library to external users, access to the library, click on Library settings > Permissions for this document library under Permission and Management.
- Click on the Stop Inheriting Permissions button.
- Click Grant Permissions > Invite People and enter your iCloud email there to add you the document library. Then an email would be sent to your iCloud mailbox, you can log into the library by clicking the link provided in that email.
If the issue persists after completing the above steps, to further check it, we need you to provide a screenshot of the error message.
Appreciate your understanding.
Best regards,
Madoc