Progress has been made. At least now it can be hotplugged and udisks will mount it under /run/media/username/volumeid and udisksctl can umount it. The technique was to add a udev rule to set properties that inform udisks to automount without elevated permissions. The udev rules may not be as appropriate as they should be.
/etc/udev/rules.d/81-udisks-lacie-rugged-ssd-pro.rules contains
ACTION!="add", GOTO="fc_end"
SUBSYSTEM!="block", GOTO="fc_end"
KERNEL=="nvme*[0-9]n*[0-9]p*[0-9]", ENV{DEVTYPE}=="partition", ENV{ID_SERIAL}="Seagate_Firecuda_*" \
ENV{UDISKS_SYSTEM}="0", ENV{UDISKS_AUTO}="1"
LABEL="fc_end"
It looks like the chain of devices that get added when plugging the LaCie in is
partition → disk → nvme ns → nvme → pcie bus
This is not a complete solution. udevadm shows that the disk is not removable. The ATTR{removable} is not writable from a udev rule as far as my attempts have gone. Unmounting the filesystem and pulling the plug generates plenty of not very graceful log entries when udev is set to debug level logging.
Something that is working differently from usb storage occurs when powering up the laptop. If the hotplug storage device is plugged in while the laptop is powered down the usb device ends up getting mounted when the user logs in. The LaCie device does not. The device nodes are made though. Unplug/plugin the LaCie after login and it does automount.
Any suggestions on how to refine this solution?