1. Set OS timezone to Buenos Aires
Expected result: "America/Argentina/Buenos_Aires"
Actual result: "America/Buenos_Aires"
See https://www.iana.org/time-zones for latest timezones. America/Buenos_Aires is obsolete and not in the latest version, America/Argentina/Buenos_Aires is correct. Issue possibly applies to other timezones in Argentina.
Repeating the same steps above in Firefox gives the expected result: "America/Argentina/Buenos_Aires".
Presumably this will fix itself once macOS and iOS have an updated version of ICU?
Unfortunately, as of now, I think the latest ICU does not handle it correctly.
This is a bug of ICU's TimeZone canonicalization.
V8 shows the same behavior, because V8 is doing similar thing to JSC, and both shows the wrong result because ICU does not canonicalize it correctly.