@SR VSP ,
If you share a SharePoint site with external users, they'll have access to everything in it, so make sure it doesn't contain sensitive content.
It’s worth noting that the external users need to have a Microsoft account or a work or school account in Azure AD from another organization.
“You can create an Outlook.com or Microsoft account with a new email address or use an existing email address from a third-party email account, such as Gmail or Yahoo, but there are certain limitations of creating an Microsoft account via third-party email address.”
You could refer to this article Using a Microsoft account with a third-party email address to view detailed limitations.
Thanks,
Echo Du
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