So: what’s happened? My concern is about old hardware like mine (Ivy Bridge) which play fine with older Kernels, also by the fact that in the Upstream the 4* Kernels are still supported for the next years.
I installed Manjaro on February 2019: during these years I tried various times 5* Kernels,: I can’t say that they play bad, but I found that 4* series make the environment snappier, eg lower boot time, greater disk I/O (not placebo, I made test with dd and with other benchmarks tools); furthermore with 5* Kernels the suspend-to-ram is unreliable and the battery life is worse: this is the reason why I have keep Kernel 4.14.
The last thing is that 5* Kernel for an unkwon reason won’t build a dkms module (8814au - wifi adapter).
Despite the linux-firmware reason I can’t get the fact that on Kernel.org, 4.* kernels are still supported until 2024; can’t Manjaro reserve or indicate a way to circumvent this? If i correctly underestand, an user can install linux-firmware-whence (obviously at his own risk since is from AUR).
Just because the older kernels are still supported by the Kernel team does not mean they are compatible with Arch Linux. Arch supports kernels 5.3 and up. The same applies to Manjaro, which is based on Arch. You probably won’t find a currently-supported Linux distro that provides such an old kernel branch.