Did you read your own code? find_set1 change parent1

ll find_set1(ll v)
{
    if(parent1[v]==v)
    {
        return parent1[v];
    }
    else
    {
        return parent1[v]=find_set1(parent1[v]);
    }
}

And your AC code surely works in C++20 too.
https://mirror.codeforces.com/contest/217/submission/151179650

And your WA code surely too not works in C++17
https://mirror.codeforces.com/contest/217/submission/151179740