
Whether you share files with internal users or external users?
Whether all users occur this issue?
Please try to share files with users in another domain mailbox, compare the result.
Check whether there are any notification emails in the Junk email.
And disable Azure AD B2B feature in your tenant, then have a test.
Reference:
https://learn.microsoft.com/en-us/sharepoint/sharepoint-azureb2b-integration
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