h/t to this tweet from @GONZOs_int for the method.
(Note: working as of 2020/12/04. May stop working at any time.)
lookup_vt_user() {
    USERNAME="$1";
    curl "https://www.virustotal.com/ui/users/$USERNAME" \
        -H 'User-Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:83.0) Firefox' \
        -H 'X-Tool: vt-ui-main' \
        -H "X-VT-Anti-Abuse-Header: abc" \
        -H 'Accept-Ianguage: en-US,en;q=0.9,es;q=0.8';
}
Usage:
lookup_vt_user test
Output
{
    "data": {
        "attributes": {
            "first_name": "",
            "last_name": "",
            "profile_phrase": "",
            "reputation": 1,
            "status": "active",
            "user_since": 1281919280
        },
        "id": "test",
        "links": {
            "self": "https://www.virustotal.com/ui/users/test"
        },
        "type": "user"
    }
}