It's really ironic after they've been telling anyone to mind their emissions. This whole issue of having to reduce fuel imports from Russia really highlighted that the EU haven't really been that green, at least not as much as they advertise.
Domestically cultivating swathes of fast growing bamboo or paulownia tree for use in wood stoves during winter could help to regrow and regenerate firewood in a way that is sustainable. The worst scenario here is for old growth forests to be targeted. Those would take decades to replace and their greater size would lead to larger quantities of carbon emissions as the wood is burned.
Not sure if they can grow bamboo well there in Germany but maybe they can just, you know, burn their trash in incinerators for electricity and just use electric heaters at home? Certain waste products can be turned to fuel, like how coconut shells are sometimes turned into charcoal, maybe they can find something there to burn rather than throw away.
In the end it'll also boil down to proper design. I've seen illustrations of houses that uses water heated by the sun to warm to home, maybe they do that there. I mean, the sun still shines during winter, except if there's a blizzard.