sorry for pushing this - I don't mean to imply what you say is not true, but would like to understand how it can be true and at the same time users like me are convinced otherwise. The internet is chock full of instructions and tutorials mentioning the default superuser is postgres, not the user's os username as far as i can tell (except for official pg documentation). Another example is the user Tim in this thread https://stackoverflow.com/questions/50883645/is-postgres-a-default-and-special-user-of-postgresql, who also seems to be convinced that they didn't name the superuser postgres.
I'm tempted to do another install on my laptop to see what happens :))
My point being that if what you say is true but runs counter to what essentially all other instructions on the internet say, it would seem prudent to mention this disparity and the reasons for it in the canonical documentation, which would be especially valuable for noobs like me.
My issue is that - at least as far as i can recall - the default superuser was already named postgres
There is no compiled-in default for the name of the bootstrap superuser. It is chosen during initdb using the algorithm described (i.e., o/s user running initdb or the name specified on the CLI)
