Big O Notation for two non-nested loops

Technically this algorithm still operates in O(n) time.

While the number of iterations increases by 2 for each increase in n, the time taken still increases at a linear rate, thus, in O(n) time.

Linear

O(n) + O(n) = 2*O(n) = O(n)

It does not matter how many non nested loops do you have (if this number is a constant and does not depends on n) the complexity would be linear and would equal to the maximum number of iterations in the loop.

It would be O(2n) because you run n+n = 2n iterations.

O(2n) is essentially equivalent to O(n) as 2 is a constant.