I can't be 100% sure, yes. However, an online search has revealed that this is a common issue and it really seems to only appear for apps that rely on dbus.
To verify this, I've ran thunar with dbus-run-session and noticed the issue immediately:
λ ~/ dbus-run-session thunar
dbus-daemon[4432]: [session uid=1000 pid=4432] Activating service name='org.xfce.Xfconf' requested by ':1.0' (uid=1000 pid=4433 comm="thunar ")
dbus-daemon[4432]: [session uid=1000 pid=4432] Successfully activated service 'org.xfce.Xfconf'
dbus-daemon[4432]: [session uid=1000 pid=4432] Activating service name='org.gtk.vfs.Daemon' requested by ':1.0' (uid=1000 pid=4433 comm="thunar ")
dbus-daemon[4432]: [session uid=1000 pid=4432] Successfully activated service 'org.gtk.vfs.Daemon'
fusermount3: failed to access mountpoint /run/user/1000/gvfs: Permission denied
dbus-daemon[4432]: [session uid=1000 pid=4432] Activating service name='org.freedesktop.portal.Desktop' requested by ':1.0' (uid=1000 pid=4433 comm="thunar ")
dbus-daemon[4432]: [session uid=1000 pid=4432] Activating service name='org.freedesktop.portal.Documents' requested by ':1.3' (uid=1000 pid=4453 comm="/usr/lib/xdg-desktop-portal ")
dbus-daemon[4432]: [session uid=1000 pid=4432] Activating service name='org.freedesktop.impl.portal.PermissionStore' requested by ':1.4' (uid=1000 pid=4458 comm="/usr/lib/xdg-document-portal ")
dbus-daemon[4432]: [session uid=1000 pid=4432] Successfully activated service 'org.freedesktop.impl.portal.PermissionStore'
dbus-daemon[4432]: [session uid=1000 pid=4432] Successfully activated service 'org.freedesktop.portal.Documents'
fuse: mountpoint is not empty
fuse: if you are sure this is safe, use the 'nonempty' mount option
error: fuse init failed: Can't mount fuse fs on /run/user/1000/doc: File exists
dbus-daemon[4432]: [session uid=1000 pid=4432] Activating service name='org.freedesktop.impl.portal.desktop.gnome' requested by ':1.3' (uid=1000 pid=4453 comm="/usr/lib/xdg-desktop-portal ")
dbus-daemon[4432]: [session uid=1000 pid=4432] Activating service name='ca.desrt.dconf' requested by ':1.6' (uid=1000 pid=4468 comm="/usr/lib/xdg-desktop-portal-gnome ")
dbus-daemon[4432]: [session uid=1000 pid=4432] Successfully activated service 'ca.desrt.dconf'
dbus-daemon[4432]: [session uid=1000 pid=4432] Successfully activated service 'org.freedesktop.impl.portal.desktop.gnome'
dbus-daemon[4432]: [session uid=1000 pid=4432] Activating service name='org.freedesktop.impl.portal.desktop.gtk' requested by ':1.3' (uid=1000 pid=4453 comm="/usr/lib/xdg-desktop-portal ")
dbus-daemon[4432]: [session uid=1000 pid=4432] Successfully activated service 'org.freedesktop.impl.portal.desktop.gtk'
dbus-daemon[4432]: [session uid=1000 pid=4432] Activating service name='org.freedesktop.secrets' requested by ':1.3' (uid=1000 pid=4453 comm="/usr/lib/xdg-desktop-portal ")
dbus-daemon[4432]: [session uid=1000 pid=4432] Activating service name='org.gtk.vfs.UDisks2VolumeMonitor' requested by ':1.0' (uid=1000 pid=4433 comm="thunar ")
** (/usr/lib/xdg-desktop-portal:4453): WARNING **: 11:38:39.911: Failed to create secret proxy: Error calling StartServiceByName for org.freedesktop.secrets: Timeout was reached
** (/usr/lib/xdg-desktop-portal:4453): WARNING **: 11:38:39.911: No skeleton to export
dbus-daemon[4432]: [session uid=1000 pid=4432] Successfully activated service 'org.freedesktop.portal.Desktop'
dbus-daemon[4432]: [session uid=1000 pid=4432] Successfully activated service 'org.gtk.vfs.UDisks2VolumeMonitor'
dbus-daemon[4432]: [session uid=1000 pid=4432] Activating service name='org.gtk.vfs.Metadata' requested by ':1.0' (uid=1000 pid=4433 comm="thunar ")
dbus-daemon[4432]: [session uid=1000 pid=4432] Successfully activated service 'org.gtk.vfs.Metadata'
dbus-daemon[4432]: [session uid=1000 pid=4432] Activating service name='org.freedesktop.thumbnails.Thumbnailer1' requested by ':1.0' (uid=1000 pid=4433 comm="thunar ")
(tumblerd:5075): tumbler-WARNING **: 11:38:40.457: Failed to load plugin "tumbler-ffmpeg-thumbnailer.so": libffmpegthumbnailer.so.4: cannot open shared object file: No such file or directory
(tumblerd:5075): tumbler-WARNING **: 11:38:40.469: Failed to load plugin "tumbler-gepub-thumbnailer.so": libgepub-0.6.so.0: cannot open shared object file: No such file or directory
Registered thumbnailer /usr/bin/gdk-pixbuf-thumbnailer -s %s %u %o
Registered thumbnailer gsf-office-thumbnailer -i %i -o %o -s %s
Registered thumbnailer heif-thumbnailer -s %s %i %o
Registered thumbnailer /usr/bin/gdk-pixbuf-thumbnailer -s %s %u %o
Registered thumbnailer /usr/bin/gdk-pixbuf-thumbnailer -s %s %u %o
Registered thumbnailer evince-thumbnailer -s %s %u %o
dbus-daemon[4432]: [session uid=1000 pid=4432] Successfully activated service 'org.freedesktop.thumbnails.Thumbnailer1'
** (/usr/lib/xdg-desktop-portal:4453): WARNING **: 11:38:44.891: Failed to get application states: GDBus.Error:org.freedesktop.portal.Error.Failed: Could not get window list
A connection to the bus can't be made
(tumblerd:5075): GVFS-RemoteVolumeMonitor-WARNING **: 11:38:47.481: Owner of volume monitor org.gtk.vfs.UDisks2VolumeMonitor disconnected from the bus; removing drives/volumes/mounts
A connection to the bus can't be made
(tumblerd:5075): tumblerd-CRITICAL **: 11:38:47.481: Name org.freedesktop.thumbnails.Cache1 lost on the message dbus, exiting.
(tumblerd:5075): tumblerd-CRITICAL **: 11:38:47.481: Name org.freedesktop.thumbnails.Manager1 lost on the message dbus, exiting.
(tumblerd:5075): tumblerd-CRITICAL **: 11:38:47.481: Name org.freedesktop.thumbnails.Thumbnailer1 lost on the message dbus, exiting.
(xfconfd:4437): xfconfd-CRITICAL **: 11:38:47.481: Name org.xfce.Xfconf lost on the message dbus, exiting.
So, the issue seems to have something to do with org.freedesktop.secrets, it blockingly waits to establish that service and I'd like to either remove the timeout duration or fix the warning.
Not sure how to do that, though. The threads over on archlinux's forum have solutions that don't seem to apply on my system, e.g. one user reported uninstalling gcolor3 helps, but I don't have that package installed to begin with.
Best,
salt