Note that the GNU/Devuan system is not part of the ROM as offered for download above. You'll have to set that up yourself.
That being said, I still use that same Debian/Devuan setup I once described in this thread:
It does not rely on Termux or any similar App-based solution. Rather, it runs in a native (rooted) chroot of LineageOS and starts in parallel to that upon boot. This is done via a Userinit script which you can download from that other post above for reference. All this relies on the native AddonSU root-management solution of LOS16, though you can certainly achieve the sam