I recently (re?)learned that “you” was the plural form and only became a formal form under the influence of French.

Basically, “you” was “ye”/“y’all”/“youse”/“yins” before any of those existed, and the others only came into existence when “you” became formal and stopped filling that niche.

And some dialects, including some very populous ones like standard British English, still don’t have a plural “you” as a result of that change of usage. The subsequent shift to being generic only cemented the problem.

“You” regains its plurality in things like “all of you”, “you all”, “you lot” (not really for the politest of company) and “you <number>” (e.g. “You four, go sit over there”) for a group of people, but on its own it’s ambiguous.