One option would be to see if there are any bitcoin ATMs left in France that do not ask for KYC. Most in Europe already ask for it but according to MiCA they have until September at the latest. With no kyc BATM you find you can withdraw up to 995€ a day, every day until the end of August. Obviously, what should be done is to declare these transactions even if they were without kyc, but people use them to avoid declaring them. That's why politicians have imposed the kyc, so that taxes don't slip through the cracks.
That is an option, but be ready to lose the amount you are trying to withdraw per day once or be prepared to show your ID after a few days of doing this. I do believe there is a law for people who particularly do this. Once you withdraw a particular amount of money, it does not matter if you did it in a single transaction or a hundred, AML regulatory institutions will be notified about your moves.
If I had an ATM, even I do not know what I would do if I had a client who kept withdrawing the maximum limit every single day for 30 days or so. It does sound and look suspicious. So I suggest something. If you do this, consider the 995 euros lost every time you start the process of selling them. Because at some point, they may ask for an ID and you have two options. Show the ID or consider it a loss and leave.
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You claim that you didn't take into account this money (2.5 btc), which means that you don't lack finances. Then you are ready to move to another jurisdiction because of these old "crumbs" left in your wallets, just to pay less taxes.
OP is likely looking for the kind of advice people like Zuckerberg would be looking for. Millionaires and billionaires are always on the lookout for more ways to avoid taxes. Unfortunately, most of us who pay the taxes are the poor. The heaviest is always on our shoulders, never on theirs.