Because ProtonMail is based in Switzerland, it is not subject to French or EU requests. But the company is still subject to requests from Swiss courts, where French police where able to lodge their request with the help of Europol. After Swiss courts approved the order, ProtonMail began logging IP information on the account, which was subsequently handed over to French police, leading to the activist’s identification and arrest.
They used to sort of “brag” about being Swiss and not being required to bend to these sorts of tactics. One presumes that foreign governments have found some sort of end run… no doubt claiming they’re investigating hot button things like “terrorism” or “CSAM”.