Stable upstream LTSP releases are offered in .deb package format in the LTSP PPA. They should work in all .deb-based distributions that use systemd, i.e. from Debian Jessie and Ubuntu 16.04 and upwards.
Currently, LTSP19+ packages aren't available in distributions, so this PPA is the only source for LTSP packages. But even when distributions do get LTSP, it's still recommended to have this PPA in your sources: when clients netboot,
ltsp init dynamically configures a lot of other packages, like systemd, network-manager, display managers, netplan etc. Some times normal distribution updates of said packages break the netboot process, and urgent LTSP updates are required to fix it.
To install the repository in Ubuntu-based distributions, run as root:
add-apt-repository ppa:ltsp apt update
To install the repository in Debian-based distributions, run as root:
wget https://ltsp.org/misc/ltsp-ubuntu-ppa-bionic.list -O /etc/apt/sources.list.d/ltsp-ubuntu-ppa-bionic.list wget https://ltsp.org/misc/ltsp_ubuntu_ppa.gpg -O /etc/apt/trusted.gpg.d/ltsp_ubuntu_ppa.gpg apt update
Note that normally Debian users should not be using PPAs. LTSP is an exception, as it only contains shell code (and a bit of python), it is interpreted (Architecture:all, no compiled binaries involved), and the .debs are tested on Debian too.