Vitamin whitening care for dull complexion. Is there a recommended combination?

Lately, my complexion has been looking dark and dull, so I'm looking into whitening functional products.

I'm cautious because products containing vitamins are effective but can be irritating.

Among the Maypure whitening line products, which one is the most gentle and effective for beginners? Also, I'm curious whether it's better to mix the whitening serum with a moisturizer, or whether it's more effective when used alone.

If you have any magical recommendations for a brightening complexion or a recommended order of use, I would appreciate your advice!