Comment by ordu

All of them need to do it. There maybe differences, like different number of versions of kernel supported, so less of backporting, but still distros have to provide fixed kernels.

With Gentoo I believe it is more fun, because of all the options gentoo provides out of a box. More kernels, more work to do.

    ls /var/db/repos/gentoo/sys-kernel/
    asahi-sources/       git-sources/         linux-next/          scx-loader/
    bliss-initramfs/     gnumach/             metadata.xml         udev-hid-bpf/
    cryptodev/           hurd/                mips-sources/        ugrd/
    dkms/                installkernel/       modprobed-db/        vanilla-kernel/
    dracut/              kci-dev/             pf-sources/          vanilla-sources/
    dracut-crypt-ssh/    kergen/              raspberrypi-image/   virtme-ng/
    genkernel/           kpatch/              raspberrypi-sources/ zen-sources/
    gentoo-kernel/       linux-docs/          rt-sources/
    gentoo-kernel-bin/   linux-firmware/      rumpkernel/
    gentoo-sources/      linux-headers/       scx/

Not all these directories are different kernel packages, but anything with -kernel or -sources at the end is.