uint8_t element assignment to uint8_t array in C++

I am trying to create a uint8_t array and try to change the first element of the array, then print it to the terminal as a string.

But, after I assign currBlock (changed block) to arr[0], cout gives an error. I tried to find the answer in StackOverflow but couldn't find a similar question. Can you help me with it?

Error: bitset::_M_copy_from_ptr

#include <iostream>
#include <sstream>
#include <bitset>
    
int main()
{
    uint8_t arr[3]{0};
    uint8_t currBlock{arr[0]};
    int flag{1};
    currBlock ^= (-flag ^ arr[0]) & (1UL << 3);
    cout << "Buffer is : " << bitset<24>(arr).to_string() << endl;
    arr[0] = currBlock;
    cout << "Buffer is : " << bitset<24>(arr).to_string() << endl;
    return 0;
}

I was expecting a print out of the uint8_t, but instead I get an error.