Help! Overwhelmed and confused (non-EU citizen on WHVisa)

It’s just enough for a couple who need to demonstrate income of 1347.88€ per month

Assuming 2x full “new state pension” which is £168.60 a week that works out at £1461.20 a month - even at € - £ parity that fits comfortably (until inflation kicks in and the UK govt refuses to index link pensions for those retired to the EU).

Whether you’d have as good a quality of life given France’s higher cost of living I’ll leave as an exercise for the reader.

A single retiree on just a UK state pension would be sailing very close to the wind as they have to demonstrate an income of 868.20€ per month from a pension income of £730.60 - needing a € - £ rate of at least 1.18€ per £

But anything on top of the state pension and you should be OK.