Learn English – How to obtain a list of compound words as nouns

All are correct.

But are the compound nouns frequently used, or is the list frequently used?

If it's important to state 'frequently', here are some possible alternatives:

If the compound nouns are frequently used:

Here is a list of frequently used compound nouns.

Here is a list of compound nouns that are frequently used.

If the list is frequently used:

Here is a list of compound nouns, that is frequently used.

Here is a frequently used list of compound nouns. (this one still slightly ambiguous)

In English there's no such thing as a plural form for an adjective or a preposition. So if you have a compound noun, like "court martial", to make it plural you should pluralize the noun and not the adjective. Hence, "courts martial". There aren't two martials; there are two courts.

Similarly, "passersby" make sense because there are two "passers", not two "byes". "Two spoonsful" because there are two spoons that are full, not two fulls that are spoon. Etc.

But "flyby" is in a different category. It is a noun formed by combining a verb and a preposition. There are not two "byes", but neither are there two "flies". Similarly with "takeover" and "shutout". There is no "inner noun" in these cases to pluralize. So it is the combined word as a whole that is a noun, and it makes sense to pluralize it as a whole word and not as a compound.