Hey folks,
Please be patient with a friendly-noob 
This is what we are trying to achieve here, step-by-step:
- We want to enable SSU. Why? So I could find out my SSU domain.
- Why do we want to find out my SSU domain? Because I need that in order to enable “developer updates”.
- Why do we want to enable “developer updates”? So that I can install .rpm packages, such as “'
flathub.flatpakrepo” or “harbour-storeman-installer-2.3.0-release10.noarch.rpm”. Without that switch, the OS refuses to install any unsigned RPM packages — official or community-maintained. - Why do we want to install those packages? Because I want to install the «Angelfish» browser, that is packed as a Flatpak. Moreover, through FlatPak, I can get the new QtWebEngine security patches automatically at the very moment KDE ships them.
Why Termux? Well, according to my very limited understanding, SSU could not be set up by the built-in Terminal. Why? Because Sailfish’s built-in Terminal is just a minimal shell emulator: no SSH client, no ip or network tools. «Termux» brings a full Linux userland (including ssh, ip addr, proper terminal emulation).
Well, I’m just a newbie so please bear with me 
I might be — and very much likely I am — wrong.
Jolla was my first and only phone back in 2015, and I never even thought about the possibility if things “just would not work”. After Jolla, I even ran an Indian «Intex Sailfish» for a while without any problems … until one day, it just ceased working… Therefore, I was very enthusiastic as I found out that a new C2 community phone is lauched out.