not() selector not working

[MatiX221]

I have this SCSS code

h1 {
    &:not(div h1) {
        text-decoration: underline;
        &.header {
            font-family: Arial, cursive;
        }
    }
}

And my visual studio code outputs this in css

h1 {
  text-decoration: underline;
}

h1.header {
  font-family: Arial, cursive;
}

but when i use https://www.sassmeister.com i get this

h1:not(div h1) {
  text-decoration: underline;
}
h1:not(div h1).header {
  font-family: Arial, cursive;
}

i dont know why this not() is not working