Hi ,
Welcome to our new Microsoft Q&A Platform.
Check this article and try the methods there on your Server 2019, even though it is aimed at Windows 10
Computer configuration > administrative templates > network > Lanman Workstation: "Enable insecure guest logons" = Enabled
http://woshub.com/cannot-access-smb-network-shares-windows-10-1709/
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Best Regards,
Candy