I have a realme 5 Pro. Honestly, the current state of officially and unofficially supported custom ROM for rmx1971 suck. PixelExperience was the last decent half-decent ROM for my device - it had some battery issues. DerpFest, crDroid and EvolutionX are all terrible for me - because I never wanted those "fancy" settings in the first place.
Right now, I'm on DerpFest, and honestly, it's terrible. The desktop and wallpaper engine is broken, the theming is all over the place and some of the contents are out of the screen. Honestly, I want something that is as close to the stock ROM, is lightweight, and gives life to older devices. LOS seems to be a good ROM, at least from the YouTube videos I've seen.
How should I go about creating a build for my device? And what should I care about while building? And how can I make my build official later on? What about the kernel? Can it be updated beyond the version that's it at right now?
Kernels for android are supplied by google in a stripped down form. The manufacturer supplies the kernel modules in binary form at the last possible moment. Without the source code for those binaries, you're working backwards trying to build software dependencies for the orphaned kernel at the time the last available kernel was built by someone with the binary. It is a unique mess for every model of a device. Orphan kernels are the mechanism used to steal ownership and deprecate devices.
Just a quick clarification, it is the manufacturer of the platform (Soc) that is responsible for the terrible code. Blame Qualcomm