according to that page and I don’t want to risk bricking the device or where I cant print using cura
The Anycubic i3 Mega can’t run Marlin, but there’s a customized version of Marlin V1.1.9 suited for the Mega. The customized version, made by David Ramiro, is based on the official Marlin firmware. It is also open source, and you can see all of the newest updates as well as installation instructions, known issues, and more on the official GitHub page.