This needs to be split into a new topic.
If you are just building an aarch64 kernel you can use your 8 core Ryzen and the aarch64-linux-gnu-gcc cross compiler. You could run into issues though if you try to install install any 3rd party dkms kernel modules.
#Install from manjaro repo the cross compiler:
sudo pacman -S aarch64-linux-gnu-gcc
#Clone the kernel repo you want to use and cd to it's directory (here for the rpi4):
git clone https://gitlab.manjaro.org/manjaro-arm/packages/core/linux-rpi4
cd linux-rpi4
#Create and save 2 files (makepkg-arm.conf & makepkg-arm)
#makepkg-arm-config:
source /etc/makepkg.conf
CARCH="aarch64"
CHOST="aarch64-linux-gnu"
export ARCH='arm64'
export CROSS_COMPILE='aarch64-linux-gnu-'
MAKEFLAGS="-j8"
#makepkg-arm script:
#!/bin/bash
DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
time makepkg -s --config "$DIR/makepkg-arm.conf" "$@"
#Make makepkg-arm script executable:
chmod +x makepkg-arm
#Start the kernel package build
./makepkg-arm
If you are building other packages that require aarch64 libs then I use distcc such as here if I was compiling locally instead of using manjaro-arm’s build server. I have my vim3 as the master and my rock64 and x86 desktop set up as slaves. The x86 uses this package from AUR: