As discussed under Mosiah 19:23, the critical text allows for either farther or further in referring to distance. Here in 3 Nephi 4:23, both 𝓟 and the 1830 edition read farthermost (spelled farthar most in 𝓟). 𝓞 probably read with an a (as farthermost or some variant spelling). Here in 3 Nephi 4:23, the 1837 edition replaced farthermost with furthermost. The critical text will restore the earliest extant reading, farthermost.
Summary: Restore farthermost in 3 Nephi 4:23, the reading of the earliest extant sources (𝓟 and the 1830 edition).