Android users can easily update apps from the Google Play Store. Since updating apps via the Play Store is technically a routine for some users, it seems that updating via the Play Store is even easier than an OTA update. Google wants to give users an easier option to update Android. Google launched "Project Mainline" to improve the way Android is updated. In Android 12, updating the operating system can be easier.
XDA's Luca020400 noted that Google is converting the Android Runtime (also known as ART) into a Mainline module that allows updates to key system components to be pushed through the Play Store. ART compiles the bytecode of Android applications into machine instructions. If Google wants to change the way Android 12 (and future versions) compiles code, it can be changed at any time instead of relying on traditional operating system updates. Users don't have to wait weeks or months for feature improvements or security fixes.
This can really affect the devices and apps you use. XDA believes that Google can provide greater app consistency. To do this, it will have to run on ART to behave the same on all Android devices. However, it will also deprive you of some of the customization features that device manufacturers used. If they configure ART for performance or flexibility, you may lose those privileges.
However, Google may consider it worth it. Android 12 can partially solve the problem of OEMs lagging behind or missing operating system updates. Of course, there is a big problem in improving compatibility. It still does not solve some problems with Android updates. However, if there is a zero-day that needs to be patched before a traditional patch is released, this new change will make a difference.
Project Mainline extends the capabilities of Project Treble. While Treble reduced OEMs' reliance on SoC vendors for each individual OS update, Mainline reduces Google's reliance on OEMs to provide security updates for key OS components. Project Mainline extends the Treble philosophy to more important parts of the Android platform, removing OEMs as dependent middlemen from the equation. The goal of Project Mainline is for Google to take control of security-critical infrastructure components and system applications and maintain development consistency separate from OEMs. Project Mainline is rightfully called the biggest change in Android since Project Treble.
