PowerShell: trying to make file readonly made it disappear

I’ve tried to make a directory ReadOnly in PowerShell, yet it disappeared instead.
How can I get it back to appear in the Explorer?

PS C:Usersjaboja> cd .Documents
PS C:UsersjabojaDocuments> (Get-Item Nextcloud).Attributes
ReadOnly, System, Directory, Archive, ReparsePoint
PS C:UsersjabojaDocuments> (Get-Item Nextcloud).Attributes += 'ReadOnly'
PS C:UsersjabojaDocuments> (Get-Item Nextcloud).Attributes
Get-Item : Could not find item C:UsersjabojaDocumentsNextcloud.
At line:1 char:2
+ (Get-Item Nextcloud).Attributes
+  ~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : ObjectNotFound: (C:UsersjabojaDocumentsNextcloud:String) [Get-Item], IOException
    + FullyQualifiedErrorId : ItemNotFound,Microsoft.PowerShell.Commands.GetItemCommand