Can you transit more than once?

Hi, I would like to book the following itinerary as a UK citizen.
London —- Shanghai (3days) —- Hanoi (7 days) —-Beijing (2days) —- London

Is this possible to use the 144 hour transit visa in both Shanghai and Beijing in this case?
Just wanted clarification that it doesn’t matter if you’re transiting back to your own home country. Also that you can use it more than once in this time period?