OxygenOS by OnePlus is among the most loved Android interfaces. Drawing its philosophy from custom ROMs like yesteryears' most popular ROM, CyanogenMod, OxygenOS features an almost-stock Android UI with several options for customization. Over the years, little changes in OxygenOS has magnified to the extent that it now has its own iconography and peculiar design elements. But if the old soul in you wants a look closer to AOSP on your OnePlus device, you can use a Substratum theme called "Out of Oxygen" to get your OnePlus smartphone's UI to look like a Google Pixel.

Substratum barely needs any introduction but if you've been out of the loop, it's a theme engine that allows you to apply system-wide or per-app themes. This app comes in handy especially for devices, like those from OnePlus, that do not come with a native theme store. Further, while Substratum usually requires you to root your phone, you can use an add-on called Andromeda to use the goodness of Substratum even without root access on your phone.

Out of Oxygen Substratum theme on XDA Forums

To install "Out of Oxygen" by XDA Member tych_tych on your OnePlus device, make sure that your phone is rooted. Then, install the Out of Oxygen APK along with the Substratum theme engine app from the Play Store, and then, follow the steps from the thread linked above.

The theme supports Android 9 Pie as well as Android 10, the developer notes some features might not be available on Android Pie. Further, it has only been tested on OnePlus devices – the OnePlus 5T/6/7 Pro – and will not run on smartphones from other manufacturers.

The Out of Oxygen Substratum theme customizes the System UI, the status bar, the OnePlus launcher, Google app, and the Google Assistant, WhatsApp, and Telegram X. It also includes certain wallpapers to go with the Pixel-like interface. Since Substratum allows modular customizations, you can choose to apply the theme only to certain elements or combine it with another Substratum theme.