The earliest text reads desirous both times here in 1 Nephi 8:12. Normally in English, “X is desirous of Y” refers to a human X that desires Y. On the other hand, if Y is desired, the expected word is desirable rather than desirous (“Y is desired”, not “Y is desirous”). For this reason, Joseph Smith edited the text for the 1837 edition by replacing the word desirous with desirable.
It is very possible that the original text actually read “it was desirable” and that during the dictation process the word desirable was replaced by desirous. One motivation for such an error would be that the word desirous had just occurred in the text (“I began to be desirous”). There is additional evidence in the book of Mosiah that desirable and desirous can be mixed up, although in this case the original reading in 𝓟 is obviously unacceptable and was immediately corrected:
Except for these two cases (in 1 Nephi 8:12 and Mosiah 8:12), the text consistently uses desirous when speaking of people’s desires (62 times) and desirable when referring to what they desire (6 times). Of those six other occurrences of desirable, four refer to fruit (1 Nephi 8:10, 1 Nephi 8:15, 1 Nephi 15:36, and Alma 32:39). So internal evidence argues that Joseph Smith’s correction in 1 Nephi 8:12 may indeed be the original text.
On the other hand, there is historical evidence for desirous having the meaning ‘desirable’. The Oxford English Dictionary (under definition 5) includes citations with this meaning from 1430 through 1796, including this example from John Gay’s The Beggar’s Opera, first performed in 1728:
Wine inspires us, And fires us … Women and Wine should Life employ. Is there ought else on Earth desirous?
Thus desirous can have the meaning ‘desirable’. Its use in 1 Nephi 8:12 does not seem that unacceptable (unlike the initial scribal error in Mosiah 8:12).
Since the earliest textual sources support desirous both times in 1 Nephi 8:12, and the second example had the meaning ‘desirable’ for the time period close to the Book of Mormon translation, the critical text will maintain desirous in “it was desirous above all other fruit”, even though this word could well be an error on the part of scribe 3 of 𝓞 (or even on the part of Joseph Smith when he dictated the text).
Summary: Maintain both occurrences of scribe 3’s desirous in 1 Nephi 8:12, even in the second case when it means ‘desirable’; such a meaning for desirous was current in the century just before the Book of Mormon translation; even so, this use of desirous could be an error based on the immediately preceding occurrence of desirous.