The Mediterranean diet itself has a lot of health benefits interrelated with the ones claimed about fish oil.

But just as a human experience, the first time I ate cod livers, it was hard to accept. Then I started spreading them on toast for breakfast, and realized that they were quite delicious, but very very much an acquired taste (and I eat almost everything).

As far as Vitamin D, there does seem to be a correlation between deficiency and severe coronavirus disease

https://www.mdpi.com/2075-1729/15/5/733

[edit] to say, I love chicken and cow liver, but it took awhile to get a taste for fish liver. Pork liver, however, is putrid. I don't think I could eat that again.