French fiscal residents pay the wealth tax once their assets exceed 790.000 Euros. If you move to France, they give you a certain amount of grace period, but after 4 or 5 years, the wealth tax applies to your worldwide assets, to the extent that the French tax people find out about them.
However, because of the nature of my work, DW and I are not French fiscal residents. If we stay in France when I/we pull the FIRE trigger, we will lose that advantage.
Although it's a pain and most other countries, including several with more "progressive" political tendencies than France, have renounced this sort of tax, it's not a huge amount of tax. It starts at 0.5%, so with our million we'd be paying €1050 per year.
Also, quite a lot of our money is in "assurance vie" schemes, which is approximately like a Roth IRA - you pay in out of taxed income, and the payout is not quite tax-free, but it's very favourable. That's massively advantageous for me, since the money which I've been putting in there has been earned while I'm not fiscally resident! So if they end up clawing a little bit of it back, I won't consider that an injustice has been done.
