I did manage to read the sensor using pigpio rather than the builtin serial interface:
sudo apt-get update
sudo apt-get install pigpio python-pigpio python3-pigpio
sudo pigpiod # start the pigpio daemon
Now I can connect the sensor to a given GPIO pin (I used GPIO24) and read the data:
In fact the Pi3 (or more precisely the SOC) has 2 UART.
See How do I make serial work on the Raspberry Pi3 or later
One is connected to the Bluetooth module the other can be used and is accessible on pins 8, 10. These can be switched but only one is accessible.
The Pi4 has 6, 4 in addition to the 2 on earlier models, but only 4 can be used due to conflicting ...