The Oppo Reno 10x zoom has three cameras on its back – one of the first ever periscopes on a phone, an 8 MP ultrawide cam and a 48 MP main camera. Unfortunately, only that last one could be used for video capture – that is no longer true as the ColorOS 7.1 update finally enabled recording using the other two cameras.
This means you can go wide or zoom in – the periscope offers 5x optical, 10x hybrid and up to 30x digital zoom. You can see this demonstrated on video by XDA Junio Member Subzuda:
Note that this works only at 1080p resolution and 30 fps. If you want to go higher, you are again limited to the main camera only (which goes up to 4K at 60 fps).
This feature is enabled in in the update with version number PCCM00_11_C.24, which is currently being rolled out in China. ColorOS 7.1 is available outside of China, though not for the 10x zoom (not yet, that is).