First method – package install via apt

This is really simple and works well; do use this method routinely:

sudo apt install ​crossbuild-essential-armhf

The tools are typically installed under /usr/bin/ and are therefore already part of your PATH; you can simply use them. For example, check out the ARM-32 gcc compiler's location and version as follows:

$ which arm-linux-gnueabihf-gcc
/usr/bin/arm-linux-gnueabihf-gcc
$ arm-linux-gnueabihf-gcc --version |head -n1
arm-linux-gnueabihf-gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0

Also, do keep in mind: this toolchain is appropriate for building the kernel for ARM 32-bit architecture, not for 64-bit. If that's your intention (building for 64-bit, which we don't cover here), you will need to install a x86_64-to-ARM64 toolchain with sudo apt install ​crossbuild-essential-arm64.