Is "research" as a countable noun actually used by native speakers?

Solution 1:

When you want to refer to a non-specific general study as "research", it doesn't need to be pluralized as the word "research" itself can mean it as an abstract noun.

When it is difficult to find usages for a word which can be used as "noun" and "verb" at the same time such as "research", you could consider searching it as a "subject" in a passive sentence:

"research has been done" vs "researches have been done" in Ngram Viewer.

There could be a situation where more than one piece of research has been done. For example, "A research" using monkeys as a guinea pig, "B research" using mice, "C research" using pigs. Then, the mass noun "research" is pluralized in:

These three researches have shown that the medicine is safe for a test on human.

or

All research has shown that the medicine is safe for a test on human.

In the second example, you don't need to pluralize "research" as the usage of "researches" indicates below.

You could consider using "piece of" to express the number of researches, but using "3 pieces of research" in the above second example doesn't seem to be ideal as it is not concise and you can pluralize "research".

You could see the plural form is rarely used in "the research on" vs "the researches on"