The error comes from VSCode trying to display that object as an AbstractArray by showing its contents in a tree view like this:

Also see Stop showing user errors for workspace in REPL · Issue #1491 · julia-vscode/julia-vscode · GitHub.
The error comes from VSCode trying to display that object as an AbstractArray by showing its contents in a tree view like this:

Also see Stop showing user errors for workspace in REPL · Issue #1491 · julia-vscode/julia-vscode · GitHub.