It was offered either for £25 or free but they kept it relatively quiet. it was fetch not push, Personally I bought my 6S from a well known UK reseller in 2018 so too late, and chances of a new payout for me are minimal. And in any case I just replaced the battery at Apple Store for £49 and yes it is better than the original. We live and learn.I'm sure I had my 6S battery replaced, courtesy of Apple at the time. Maybe a recall?
Either way, never had a problem with that phone. I used it for years.
The idea of compensating iPhone X owners is fantasy.