Here’s a simple test for historical DST transition support in IE, which exposes a gap in support for America/Chicago as recently as 1986, which we would need to support in order to allow entering something as commonplace as a birthdate.\
What we’re going to do is create a date object for 1:30 am, on April 27, 1986 (30 minutes before the spring forward transition), and add one hour to it, which should give us 3:30 am (since the 2:00 to 3:00 hour is skipped).
Open https://date-fns.org/docs/Getting-Started in IE, and paste this line into the console:
dateFns.getHours(dateFns.addHours(dateFns.parse('1986-04-27T01:30:00', 'yyyy-MM-ddTH:mm:ss', new Date()),1))
On its own, date-fns uses the built-in date object, which does not correctly support the DST transition time (it assumes the transition already happened earlier in the month, because it is back-filling from a starting point after the DTS transition date was changed, because its internal tz database doesn’t go back that far).
Then go to https://momentjs.com/timezone/ and paste this line:
moment.tz('1986-04-27T01:30:00', 'America/Chicago').add(1, 'h').get('h')
Since moment has a full tz database, it handles this correctly.