I don’t know that this necessarily changed recently, but I can confirm that most snaps using the home interface cannot read user’s home directories as root. This is by design, and snaps that need to access user files in $HOME, etc. as root, should use the read: all attribute for the home interface. See Home access as root from confined snaps
Also, fun fact, you can use -c ... instead of <<< here:
$ snap run --shell hello-world -c "echo shells are fun"
shells are fun