Is 'the majority of' singular or plural?

Like the words some and most, a premodifying phrase like the majority of is in and of itself neither singular nor plural. It has no number.

The noun it is modifying continues to function as the subject for purposes of agreement with the verb. This allows then for both possibilities:

1. (The majority of) the water is safe to drink.
2. (The majority of) the bottles are safe to drink.

Notice how adding the majority of doesn’t change anything in those two examples.

Therefore because studies is plural, so too is the majority of studies:

The majority of fund studies have agreed that a common attribute for superior performance is due to managers’ skill.

That’s because it just means most fund studies; the number does not change.

For US English users who often look to Merriam-Webster Dictionary as a reference, this is a very helpful resource: https://www.merriam-webster.com/words-at-play/majority-of-singular-noncount-nouns-usage-minority

Their conclusion:

The question then arises: do majority and minority take a singular or plural verb? The answer is most often determined, again, by the countability of the noun being apportioned: A majority of the voters are in favor of the law. The majority of the wine is from Argentina. A majority of the songs feature her on guitar. A majority of my day is devoted to keeping records. A majority of my work hours are devoted to keeping records. A majority of the workforce is categorized as blue-collar.