Here the 1858 Wright edition replaced those with these, probably unintentionally. The original those was restored to the RLDS text in the 1908 RLDS edition. In this chapter, Alma seems to have the plates and other artifacts (like the Liahona) before him as he speaks to Helaman (Alma is handing over these objects to his son); thus we find the use of these elsewhere in this chapter:
On the other hand, those is never otherwise used in this section of Alma’s discourse to refer to these objects. Presumably the twenty-four plates (containing the Jaredite record) would have been in Alma’s possession and present. So it is possible that the unique use of those here in verse 21 is an error for these. There is considerable evidence that the scribes occasionally mixed up these and those (for a nearby example, see under Alma 37:29). Nonetheless, those will work here in Alma 37:21, especially since here Alma brings up a new topic (namely, the Jaredite plates); the shift from these to those allows the shift in topic to be more prominent. Another possible reason for the use of those here in verse 21 is that these particular plates, given their sensitive nature, may not have been actually present. Note that Alma later explains to Helaman that he must keep back all the specifics regarding the Jaredites’ secret abominations:
Since those will work here in verse 21, the critical text will follow the earliest textual sources and maintain that unique occurrence of those. In general, the text allows for variation between these and those, as in the following pair of examples, also occurring in this chapter:
Summary: Maintain in Alma 37:21 the demonstrative determiner those, the reading of all the earliest textual sources, including 𝓞: “and now I will speak unto you concerning those twenty-four plates”.