nixos

That being said, the statement that symbol conflicts do not exist on other distros is plainly not true.

I have never claimed such a thing.

Classical distros have exactly one instance of a library ABI's .so in most cases which is usually the only place where any given symbol is defined.

You could technically provoke a symbol conflict using LD_PRELOAD and the like but it's not something you commonly run into because package upgrades always replace the previous version entirely.

You could technically have multiple conflicting sos on classical distros too by prefixing a more detailed version but you don't; doing such things kinda what differentiates Nix from classical package management.

This QT issue in particular was an impurity (working outside of Nix' pure model; not as intended) caused by "installing" qt libraries into your environment imperatively (which isn't something you should do anyways) that was solved a couple years ago.

No, the actual issue was an impurity (not working in Nix' pure model). Impurity is a bug; it was fixed years ago.