That’s the problem with mixing discussions on auto mounting in Thunar with shared folder.
Thunar auto mounting: that should be possible without root. I don’t know how exactly that works but might be SUID something, pkexec, /etc/sudoers.d (unlikely).
And SUID Disabler and Permission Hardener is nowadays enabled by default.No: SUID Disabler and Permission Hardener is not yet enabled by default. That forum thread will be updated when this happens.
Thunar - ArchWiki says
While Thunar supports automatic mounting and unmounting of removable media (gvfs package is required)
Check if gvfs is installed. To install:
sudo apt install gvfs
Reboot might be required. Please see if that helps.
Quote Debian -- Details of package gvfs in buster
userspace virtual filesystem - GIO module
gvfs is a userspace virtual filesystem where mounts run as separate processes which you talk to via D-Bus. It also contains a gio module that seamlessly adds gvfs support to all applications using the gio API. It also supports exposing the gvfs mounts to non-gio applications using fuse.
This package contains the GIO module that lets applications use gvfs mounts.
From:
apt-cache show thunar
Also any of these packages might be missing:
default-dbus-session-bus
dbus-session-bus
gvfs
policykit-1-gnome
polkit-1-auth-agent
thunar-volman
tumbler
udisks2
xdg-user-dirs
libcairo-gobject2
libpangocairo-1.0-0
libxfce4panel-2.0-4