There are several places in the 2e Alpha where "folks" is used and sounds funny - 14 by my count. In keeping with Tolkien's usage, TOR rules should default to using "folk" without the s, and only use "folks" in rare cases that refer to groups of individuals rather than aggregate members of a culture. Edit: Folk is appropriate whether referring to one culture (Durin's Folk) or multiple cultures (the Free Peoples of Middle-earth can also be expressed as the Free Folk).
One reference (https://oneminuteenglish.org/en/folk-or-folks/) puts it this way: “Folk” is a collective noun and refers to a group of people in general. “Folks” is a group of individuals. (To Anglophone ears, "Free Folks" sounds funny because we have internalized this distinction between groups of people and groups of individuals.)
Keep "folks" here:
p. 40 "that many folks mistake for lack of courage." (Here folks can be understood to mean individuals rather than other peoples of Middle-earth.)
p. 107 "allows to filter other folks' reaction ..." (Here again folks is appropriately referring to groups of individuals)
Replace "folks" with "folk" here:
p. 11 "distant realms and the folk who inhabit them"
p. 29 under NAME: "various folk of Middle-earth"
p. 30 "The language of most folk inhabiting ..."
p. 34 "at odds with other folk"
p. 35 "members of other folk"
p. 38 "the way other folk do"
p. 66 "as diverse as the folk that craft them."
p. 72 "Impoverished folk are probably suffering ..."
p. 82 "has even led other folk to believe ..."
p. 108 "the folk inhabiting it"
p. 123 "other folk struggle to appreciate it"
p. 163 "if the item is known by different folk."
p. 164 "the treasuries of most folk"
p. 169 "Distant folk grow suspicious ..."