I've made the correction and moved the ruleset definition before the include.
Note
To make this work, the user has to delete the files /config/rsyslog.conf and /config/rsyslog.cfg from the USB device.
Reboot the server and reconfigure the syslog service in the GUI again.
I modified SMB Extra to:
#unassigned_devices_start
#Unassigned devices share includes
include = /tmp/unassigned.devices/smb-settings.conf
#unassigned_devices_end
[global]
spotlight backend = tracker
[Media]
path = /mnt/user/Media
spotlight = yes
… rebooted Unraid 6.9.2 and spotlight search seems to be working again in macOS Finder over SMB! I haven't examined logs for potential adverse events but will do in a little while.