Looking at the figures in the paper, cooking for 4 minutes (which is way overkill for spinach leaves) decreases lutein by 25-50% (with relatively large error bars).

I haven’t done the math in how much lutein is in spinach vs how much we need but to a first order of approximation that’s acceptable.

In the abstract they say they cooked spinach for up to something absurd like 60 minutes. Spinach leaves are cooked within a minute or so in my experience, so not sure why they performed the study that way.