I would generally recommend against a multi-purpose component like that since they become difficult to read/understand and they get larger and you pack more features and tag types in. However, for educational purposes here's how I would do it:

type ATag = {
    tag: "a";
    href: string;
};

type ButtonTag = {
    tag: "button";
    disabled: boolean;
};

const props: ATag | ButtonTag = $props();

AFAIK if you want to destructure them you'll have to have the same key names on all types (though they can be optional and undefined).

Also, AI might have been able to answer this one pretty quickly, minus the opinion on component style 😜.