Arthur Chris Eccel argues that Book of Mormon "Josh" has not been attested as an authentic Semitic name.
Arthur Chris Eccel, Mormon Genesis (Hilo, Hawaii: GP Touchstone, 2018), 541
Josh (Claim: the form y’š has been attested. This should be vocalized jōš and considered to be the hypocoristic form of Josiah [jōšiyyāhu]).
Comment: Avigad/Sass indicate that the verb root is ‘wš, and that the name should be vocalized yo’aš (Josah), a name that occurs many times in Judges and 1 and 2 Kings. The vocalization is not indicated in the inscription. The aleph (glottal stop) is a root letter, not a device to indicate a vowel. If it were, aleph would normally represent ā. In any case, Josh, as an English shorter form for Joshua, may be as far as we have to look for this BOM name.