The issue was folder not created correctly.
The guide is not clear on how to create the “shared folder” instead of a simple folder. Please update the tail-drop page on how to create a shared folder and give read and write permission to tail-scale user.
I would like to see the new documentation for this too. When I followed the instructions on creating the new shared folder, I went back to Properties, Permissions and I see no system user named tailscale. Only Administrators. I do have the 1.22 version of Tailscale installed on this Synology also. I was able to read deeper into the instructions and discover that the issue was ambiguous wording. I WAS able to choose tailscale system user from the drop down on that Taildrop, Property, Permission, CREATE field. This could be described better. Hope this helps.