'Miscellaneous': must be followed by a plural count noun

Solution 1:

Because Garner is writing about English, the use of the Latin source word is irrelevant. I’m not sure whether Garner is correct, or what the basis of his statement is (the entry does not tell us), but determining the accuracy of the statement requires research into actual English usage.

The Oxford English Dictionary indicates that Garner's statement has not been true throughout the history of the word; its first definition for miscellaneous is as follows:

With a singular noun: consisting of members or elements of different kinds; of mixed composition or character. With a plural noun: of various kinds.

In fact, most of the OED citations are with singular nouns, including the latest one (from 1986):

A. Massie Colette ii. 31 Willy..embarked on the muddy waters of literary journalism and miscellaneous hackwork.

Perhaps the 35 years since this book's publication have seen a change in the use of miscellaneous; perhaps Garner has overlooked some cases, or perhaps he is trying to push usage of the word in a certain direction based on his own preferences.

I think "must be followed by a plural count noun" goes a bit too far. To me, expressions like “miscellaneous furniture”, “miscellaneous cutlery”, “miscellaneous jewelry” sound all right.

“Kindnesses” in the plural usually refers to kind actions, while “kindness” in the singular usually refers to a quality or state. As Edwin Ashworth commented, that topic deserves a separate question post.