I am going to retire in S of France. after that I wont be able to buy and sell, so my BRKB holdings should let me eat and drink red wine quite well there :-) USA brokers will only let is sell down....

If you're retiring in the south of France (where I am sitting at the moment!), presumably you will be a resident of France for tax and other purposes unless you're visiting for shortish periods. (still having to file in the US too--separate discussion). If that's the case, you will be allowed to use any broker which serves French residents, which includes Interactive Brokers, various banks, and wealth management banks. Many of those will be just fine with you buying and selling US stocks and options (though not mutual funds or ETFs). You'll be able to move your stock from your US broker to whatever new France-supporting broker you pick, and do whatever trades you like in it.

The tax situation is bad, of course. France has immense payroll taxes. As they are not fond of capitalists, to say the least, any profit on a stock sale is kind of deemed as income in this sense so you have to pay not only the capital gains rate income tax on the profit, but also the "social charges" (payroll tax) on it as well. I believe they have simplified this recently and made it a single combined flat number and lowered it somewhat, but it still isn't exactly a SMALL flat number...30% I think??

Jim