Here scribe 3 of 𝓞 may have omitted the subject pronoun I, which Oliver Cowdery supplied when he copied the text from 𝓞 into 𝓟. We have already observed several cases where scribe 3 omitted—or may have omitted—the pronoun I (see the discussion under 1 Nephi 5:8).
But it is possible to read the text here in 1 Nephi 8:11 without the subject. Perhaps Oliver Cowdery felt that there was just too much distance (namely, four intervening words) between the preceding verb partook and the conjoined “and beheld”, so he added the I. He may have also been influenced by the example two verses earlier where the subject pronoun I had been supralinearly inserted (see 1 Nephi 8:9). The 1830 typesetter further isolated the last clause from the former clauses here in verse 11 by punctuating the break with a semicolon rather than with a comma.
Typically, there are no intervening words when beheld is conjoined with a preceding predicate, as in the 14 cases of “looked and beheld”, of which 13 are found in 1 Nephi 11–14. (The 14th is in Jacob 5:17.) Nonetheless, it should be noted that there are three cases of “I looked and I beheld” (in verses 24, 30, and 31 of 1 Nephi 11), which shows that we can get variation regarding the repeated subject even when the verbs are near each other.
Besides the example in 1 Nephi 8:11, we have two other examples where there is an intervening direct object before a conjoined subjectless clause beginning with beheld:
The first of these two examples is also in 1 Nephi 8, which means that we have the same scribe as in verse 11 (namely, scribe 3 of 𝓞). Thus one could speculate that the subject pronoun I might also be missing in verse 26. Nevertheless, none of these three examples seem incorrect, not even especially awkward, which means that we have no strong reason to reject “and beheld” in 1 Nephi 8:11, 1 Nephi 8:26, and Helaman 5:30.
Summary: Restore the reading of the original manuscript in 1 Nephi 8:11 (“I did go forth and partook of the fruit thereof and beheld that it was most sweet”); the semicolon after thereof will also need to be removed; the lack of the repeated subject is also found in similar constructions elsewhere in the text (such as 1 Nephi 8:26 and Helaman 5:30).