The text has occasionally been edited to avoid singular-plural combinations such as much modifying a plural count noun. Here in Enos 1:21, an original much horses was edited to many horses in the 1837 edition. Similarly, two cases of much people have had the much edited to many, again in the 1837 edition:
For the example in Mosiah 29:7, Hyrum Smith (the scribe in 𝓟 for that passage) wrote mtch ‘much’. The 1830 typesetter crossed out mtch and supralinearly penciled in many; even so, he ended up typesetting much, with the result that for the printed editions, many showed up first in the 1837 edition.
Sometimes the much has been maintained and the plural count noun has been changed to the singular, especially when the noun can be considered noncount:
Yet in half the cases, the original “much ” has been retained, including instances of much people and much afflictions:
The critical text will restore all those cases where an original “much ” has been removed from the text (usually by editing).
Summary: Restore the original much horses in Enos 1:21; instances of “much ” were fairly common in the original text.