I'm told from other forums that the deprecation of basic authentication WILL effect this method of authentication.
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SharePointOnlineCredentials supports Kerberos, Ntlm and basic authentication. So it will not work with SharePoint online after basic support is dropped. For SharePoint online you should be switching to access tokens.
With access tokens you call the azure ad to get the token. If you want a user token, then a web browser is used to login to ad and get the token. You can also use an application clientid and secret (know as password flow) to login as an application (not a user) without a browser.
see docs
https://learn.microsoft.com/en-us/sharepoint/dev/sp-add-ins/using-csom-for-dotnet-standard