I've managed to solve the back button problem on my phone (Moto G7 Play).The problem was that I had initiated "One-button nav" when setting up the phone.
This results in a bar at the bottom of the screen which can be swiped left and right, however, it does not work as well as a back button/arrow.
I managed to switch off the One-button display and return to having three buttons at the bottom of the screen, similar to my previous Moto g4.
One of these is a back button and now woks as it should on Chrome.