It will be isolated in its own directory, as I said I think distrobox.it+neon+, own home will be a far better solution of course. I keep hearing Flatpak is adding snap-like deeper features so I wondered how far it went. About the KDE 6 being unstable: I think they wanted to ship something out and for people preferring stability, 5.x LTS will be there for a long time.
It was a serious issue back then. People were wandering around on the Internet with root accounts. A lot of #linux IRC channels were kicking&banning anyone with “~root” or “root” ident with educational sentence like “Do not use root account as your ordinary account, check instructions”. We don’t see the issue widespread today since distros did very good intended “dark patterns” to push users to regular user accounts. Linux (or UNIX) “root” account is true god mode. E.g. infamous “rm” as root joke (!) could even affect Windows running WSL2, so MS had to implement special workarounds.