Firearms are definitely ownable in Germany...it may take some hoop-jumping, and have certain restrictions applied (like you may not be able to own military calibers...I understand that M1 Garands rebarreled for .270 Winchester are popular as a result), but it can certainly be done within the law.
And then there are all the guns that they just plain have...”allowance” be stuffed. I remember a post from somebody on this forum, ages ago, who said that when he served in the US Army in Germany in the 1960s or 70s, he got to know many of the farmers around his base...and *every* one of them had a GI-issue .45 pistol with the serial number removed. And he said that, in all cases, that was just for starters....
In the 1980’s. I’ve heard stories where some Germans might have buried WWII era weapons like MG42’s, FG42’s and Mausers in case of a Soviet invasion. Who really knows but there are always ways to get past the laws.