In apparmor profile:
dbus (receive)
bus=session
path=/webbrowser_2dapp_5fwebbrowser_2dapp_5fx4
interface=org.freedesktop.Application
member=Open
peer=(label="snap.unity8-session.unity8-session"),
In journalctl:
Feb 09 16:04:32 drumbo dbus[23950]: apparmor="ALLOWED" operation="dbus_method_call" bus="session" path="/webbrowser_2dapp_5fwebbrowser_2dapp_5fx4" interface="org.freedesktop.Application" member="Open" mask="send" name=":1.68" pid=24332 label="snap.unity8-session.unity8-session" peer_pid=3207 peer_label="snap.webbrowser-app.webbrowser-app"
Feb 09 16:04:32 drumbo dbus[23950]: apparmor="DENIED" operation="dbus_method_call" bus="session" path="/webbrowser_2dapp_5fwebbrowser_2dapp_5fx4" interface="org.freedesktop.Application" member="Open" name=":1.35" mask="receive" pid=3207 label="snap.webbrowser-app.webbrowser-app" peer_pid=24332 peer_label="snap.unity8-session.unity8-session"