I want to try to port a new kernel for mobile phones

I’m using Motorola Moto Z2 Force. Since the flash memory of this old phone is only 64G, it is completely insufficient now.
So, I want to try the compression function of F2FS, but the 4.4 version of the ROM kernel seems to be too old, and F2FS does not support compression. Some of my ARM development board kernel experience tells me that if U-BOOT lacks certain functions , It is very likely that the kernel will not be booted, is it the same for mobile phones?
And, the ROM kernel source code seems to include some OEM-provided drivers. Can these drivers be copied to the Linux 5.14 source code? Can they be compiled normally?

I don’t know how the kernel you are working with works, or how your device boots. I don’t actually know the device.

Yes. If uboot is missing a function that the kernel relies on, it could end with a device not booting.

Likely not without a big porting effort. A lot has changed in the kernel from 4.4 to 5.14, so you would need to port the drivers in question to the new mainline stack.

It sounds terrible, so will the workload of reverse porting the new F2FS to the old 4.4 kernel be a little less?

No idea. I don’t work with BSP kernels, so I don’t know how hard it is to backport stuff.