I think the statistics speak for themselves. There were exactly two famous incel terrorists aka Elliot Rodger and another guy whose name I don't remember. They both lived in the US and honestly the only thing that connects them with other shooters is that they had guns.

This type of terrorism did happen in Germany i.e. the "Halle" shooter, but he had to rely on homemade weapons with his own black powder ammunition and his attack failed, because his guns weren't strong enough to breach doors at a synagogue. What he did do is shoot a random woman passing close by (less than 5m distance) who was angrily glaring at him and then he went to a random kebab shop to shoot up an immigrant, before the police caught him.

It's really mostly a matter of keeping guns away from people who shouldn't have access to them.