It's a bit of a bummer that the OnePlus 7 is only able to stream Netflix at 720p "HD" — that's just one quarter of the full 1440p resolution of its beautiful display, after all. But if you decide to unlock the bootloader for future root/ROM adventures, then you'll have to make do with just non-HD 480p Netflix streams.
For the unfamiliar, Netflix and some other services like Hulu and Amazon Video use a Google-provided DRM solution called Widevine, which has multiple levels of security. A higher "L1" level of Widevine is required by Netflix for 720p HD playback. For a while, OnePlus phones didn't even support L1, though all phones since the OnePlus 6 have shipped with it. And like its predecessors, the OnePlus 7 Pro loses that L1 support if the bootloader is unlocked. In such cases, the devices fall back to (insecure) Widevine L3, which Netflix only uses for lower-quality 480p playback.
Not all devices lose Widevine L1 when the bootloader is unlocked — for example, the Pixel 3 XL last year — but OnePlus devices do, and based on reports, the 7 Pro is no exception.