Just upgraded to MS server 2019 essentials and we use a Western Digital MyCloud to run back ups too. Unfortunately I'm now not able to connect 2019 to the NAS due to the Group polices and comes up with the warning: "You can’t access this shared folder because your organization’s security policies block unauthenticated guest access".
So it appears that I need to disable this policy (I'd rather not but can't see another way round), only problem with that is all the instructions I can find are for the 2016 server and it's changed for 2019.
Open GPO editor
Move to Computer Configuration -> Administrative Templates -> Network -> Lanman Workstation and select Enable insecure guest logons