Here Oliver Cowdery initially wrote “the mysteries”, but then he immediately added “of God” supralinearly without any change in level of ink flow. Although this addition could be an emendation, it doesn’t seem likely. The Book of Mormon text rarely refers to the mysteries of God as simply “the mysteries”. (For one example that could be interpreted this way, see Alma 37:4.) Normally in the text we get “the mysteries of God” (eight times) or “his mysteries” (four times) or “the mysteries of him” (once, in Jacob 4:8). Nephi himself uses only the phrase “the mysteries of God” (in 1 Nephi 1:1 and 1 Nephi 10:19 as well as here in 1 Nephi 2:11).
Summary: Maintain in 1 Nephi 2:16 “the mysteries of God”, the corrected reading in 𝓞; the Book of Mormon rarely refers to God’s mysteries without specifying that they are indeed his.