Go's quite horrendous and limited type system makes it a poor fit for everything. The worst thing about Go is, in fact, the language. Everything except the language redeems it.
I agree- multiple return values don't compose; errors are better than exceptions, but still super verbose; channels have a lot of foot guns; enums are just sad. But despite all of that the language has some really good qualities too- interfaces works far better than it feels like they should; the packaging fits together really well (I'm learning Rust right now and the file structure is far more complicated); and peop…
There isn't much more you can do with them. Literally all an enum can produce is a number.
In increasingly common use in a number of languages, enums are being coupled with discriminated unions, using the enum value as the discriminant. This is probably what you're really thinking of, noticing Go's lack of unions.
But where you might use a discriminated union if it were available, you would currently use an interface, where the type name, rather than an enum, is what differentiates the different types. If Go were to gain something like a discriminated union, it is likely it would want to extend upon that idea. Most especially given that generics already introduced syntax that would lend itself fairly well to it:
type Foo interface {
Bar | Baz
}