A few quick things, no login and nothing that identifies you. Get an honest first look at the lifestyle your savings could support, and whether the money lasts.
Your monthly spending power in France on about $1M
A lean lifestyle in France
Day to day, that looks like a small apartment in a lower-cost town, transit or one older economy car, cooking at home with the odd cheap meal out. For health, the public health system, with out-of-pocket costs a real worry.
As a US citizen, you keep filing US taxes wherever you live.
France: US treaty: exemption method (US retirement income taxed by the US only)
This is a fast estimate, not the full simulation, and not financial advice. It only flags the tax question. The full plan works out what you'd actually owe on each side of the border. It also models real balances, every account type, and healthcare, year by year.