You can do su to change the user in the current shell. Afaik it just defaults to root if no user ist specified. Everytime you run su you actually do su root
That said I always thought that it stands for switch user so intereresting to know that it‘s substitute.
I still use my Pinebook Pro as daily driver (next to a desktop pc) and I‘m actually quit happy with it. It’s not the most powefull machine but it does it‘s job.
Also I never really experimented with all the special distros. Nowadays I just run plane Debian on it and everything seems fine.