How "to remove everyone from all non-default shares" you asked already and you got an answer on this:
You can add authenticated users with full control to the shares with the following cmdlet: Grant-SmbShareAccess
More details you will find here: https://learn.microsoft.com/en-us/powershell/module/smbshare/grant-smbshareaccess?view=win10-ps
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Regards
Andreas Baumgarten