I haven’t seen anyone put anything together for PureOS specifically. But since PureOS is based on Debian, I’m sure someone has put something together for LFS on how to build Debian. Just search for something like build debian from scratch.
thank you for starting this thread i’d be also interested in anything from scratch as it doesn’t have to be FSF RYF certified.
the RYF certification is ONLY for individuals/entities that wish to distribute the OS they “built” and maintain but it is not a legal requirement if you wish to keep it to yourself and just use it privately for education or anything-else. it is however encouraged to share but not MANDATORY. this is about freedom and free-software has made this abundantly clear with the GPL and the one concerning public open-hardware documentation.
the copyleft exists to protect and prevent interesting/inovative random/unlicensed public open-source code from “falling-into-the-wrong-hands” and getting copyrighted/locked-down/controlled by proprietary-software companies and used against the public good.