Hi @Ramruthan, R. (Rakesh) ,
Welcome to Q&A forum!
Unfortunately, the maximum number of SharePoint Online sites that can be shared externally by a single tenant is not yet officially specified.
However, external sharing may be restricted by domains or security groups, and guest access may expire after a specified period of time.
You can follow the information in the Message center to get relevant information as soon as possible.
For your reference:
https://learn.microsoft.com/en-us/sharepoint/collaboration-options#external-sharing
Good day! :-)
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