Yes, we call that a thermonuclear bomb. The only problem is that in order to detonate a thermonuclear bomb you need a nuclear bomb to ignite the Fusion reaction first. Civilian/Generative Fusion can never be weaponized the same way nuclear fission has been. Fusion only occurs under the most extreme temperature and magnetic conditions, if they vary even slightly the fusion process stops instantly and you get no energy. We can barely get a energy positive fusion process working in a reactor with all the best tech in the world. Barely. It cannot and will not ever be weaponized the way you think.

Any fusion reactor in this century will likely be putting out a Lot of fast neutrons. These fast neutrons can turn otherwise benign heavy elements into weapons-grade fissile material. There are detection techniques for this kind of breeding and I’d imagine any country capable of building a fusion reactor would also be okay with audits. If you just want weapons-grade fissile material, there are far more economical avenues than a fusion reactor.

Also, if fusion reactors become more viable than fission reactors, then we could put a global ban on all fissile materials. They would serve no purpose except for weapons.

It already is. Hydrogen bombs.

https://en.wikipedia.org/wiki/Thermonuclear_weapon

The largest non-thermonuclear bomb was only 500 kilotons yield.

The largest thermonuclear bomb was 50 megatons. 100x.

Any ordinary piece of lumber could be used as a weapon or to build a house.

Unlimited energy makes rail guns really nice.

No.