Adding or compounding returns

Hye guys, this seem not straightforward at all to me: when should I add and when should I compound returns? It makes a lot of difference, especially if you have to select a suitable portfolio among many. For example I got an answer wrong because I added returns and I selected a portfolio with higher Sharpre ratio, while compounding returns that portfolio was not suitable anymore becuase it wasn’t even meeting the minimum return requirement

When in doubt, compound.