That's basically the same thing as using an interface. An interface is just a more formal way of declaring it.
The difference IMO is that the interface is still a nominal declaration. With it you have a named type, while the alias is purely structural. in TS/Flow I prefer to use the type alias ubiquitously, however in other typed languages I prefer being more nominal. In Purescript, which supports both methods also, I almost always fully declare the type.
TypeScript interfaces are purely structural. The effect on the type system of using `interface Foo { … }` vs `type Foo = { … }` is the same. I mean, the whole point of interfaces in TypeScript is that it's structural typing, and if you want nominal typing you use a class.
The only difference is readability and how tools like VSCode treat it (e.g. if you hover over something typed as an `interface`, VSCode just shows the interface name, though you can hold a modifier to see the whole definition).
All that said, if you want to exclusively use type aliases, you're certainly free to do so. But I expect most TypeScript developers will consider that to be a bit odd.
It affects things like previews / mouse hovers in editors like vscode, too. Interfaces will show the interface name, types will show the structure.
type MyType = { a: number, b: string };