In a statement, Paris prosecutor Laure Beccuau confirmed all the charges and said the investigation is moving forward. The fact of Durov being placed under formal investigation means he is formally suspected of what he’s been accused of.
In the French judicial system being placed under formal investigation is a necessary procedural step in order to take a case to trial. However it does not mean a trial is certain. If authorities decide they don’t have a strong enough case the investigation could be shelved before it gets to court. But the step means there’s a substantial reason to pursue a probe.