Well, the delivery got lost in the mail so I ordered some more and that second batch turned up.
But you're right, these don't seem to be a straightforward GATT interface with temperatures that are directly readable by nRF Connect. It's like Tuya has encrypted the process so that the devices only work with their proprietary software. That might explain why there is a(t least one) GitHub project for replacement firmware for the device.
When I've got more time I'll have another poke around, but don't hold your breath, might well be Christmas-New Year.
In the meantime, the devices are still useful as basic digital thermometers, even without the Bluetooth connection.