include <bits/stdc++.h>

You manually added the conquer cost for the first city (index 0) and started recursion from index 1. This led to missing the current city's cost in the recursive steps and caused incorrect handling of the initial city.

Try this

#include <bits/stdc++.h>
using namespace std;
using ll = long long;

ll Min_dist(ll capital, ll n, ll conq, ll a, ll b, vector<ll>& arr) {
    if (conq >= n) {
        return 0;
    }
    ll current_cost = b * abs(arr[conq] - capital);
    ll option1 = current_cost + Min_dist(capital, n, conq + 1, a, b, arr);
    ll move_cost = a * abs(arr[conq] - capital);
    ll option2 = current_cost + move_cost + Min_dist(arr[conq], n, conq + 1, a, b, arr);
    return min(option1, option2);
}

void MYFUN() {
    ll n, a, b;
    cin >> n >> a >> b;
    vector<ll> arr(n);
    for (auto &it : arr) cin >> it;
    cout << Min_dist(0, n, 0, a, b, arr) << endl;
}

int main() {
    ll t;
    cin >> t;
    while (t--) MYFUN();
}