Officially it’s allowed after April 17th, but there’s already an extensive list of approved devices.

https://www.test-aankoop.be/woning-energie/hernieuwbare-energie/nieuws/plug-and-play-zonnepaneel

There’s probably a french version of that article as well, but test- achats/aankoop hasn’t made it easy to switch languages :)

These plugin systems shut down automatically when there’s a power outage. To make sure that they really do shut down when needed, in Belgium only plugin systems that have been approved by the network management organisation may be used. The other countries that allow these probably have similar precautions.