OnePlus appears to be working on a software feature that will force dark mode on apps that don’t support it otherwise. XDA Developers found a new option in code for the latest OxygenOS Open Beta 11 that adds an override toggle in settings:

Android 10 already has this built in as part of the hidden developer settings that most people won’t ever know about or unlock on their devices, but if OnePlus implemented it into its next version of Android, it could be different to Google’s and potentially better built.
It means we might see this as a stand out feature in the rumoured OnePlus 8 series of phones. Despite the recent disruption to smartphone release schedules as the coronavirus pandemic spreads across the globe, the phones are hopefully still to see a release in the next few months, sticking to the company’s six month update cycle for its line up.
XDA said after it found the toggle it couldn’t get it to work, but it’ll be welcome addition if we see it soon. The prospect of it coming to older OnePlus phones is a plus too.
Dark modes are considered desirable for not only changing the look of your phone’s system and not blinding you at night but also as a battery saver. Blacks on an OLED display use far less battery than bright white ones.