I’m not sure how a [...] laser confinement reactor translates to nuclear weapons.

Well, that's your lack of imagination or domain knowledge, or both.

As it happens in current political climate, you can't just pull out a half megaton thermonuke and test it over some desert or atoll. The second best thing is simulating the entire thing as well as you can and that's what all countries that have thermonuclear weapons did after testing was banned. Probably the most open and transparent about it is France, with them stating that they did just that, complete with their own NIF-like facility.

Inertial confinement fusion experiments (which can be achieved by squeezing it with single current pulse like Z-machine or, better yet, heating with lasers like in NIF) mimic closely conditions within secondary stage of thermonuclear weapon, but it's more to it than fusion. Compression of capsule involves ablation of external layer - rapid evaporation pushes the rest of capsule inward, then hydrogen is compressed and ignites - again, not a simple process, because things happen so rapidly that there's not even a single temperature that can be ascribed to that plasma; then capsule and plasma interact - again, nothing is simple about it, because denser medium is on the outside, that means any imperfections will start turbulent mixing, something you want to avoid. Then, you can measure how materials behave under this intense 14MeV neutron and gamma pulse, something they do and something that's more useful for military purposes

You can't simulate (reasonably accurately anyway) these complex phenomena out of first principles, but you can make minuscule diorama and measure it. That's what NIF is for, with the only differences being 1. scale and 2. that NIF uses UV and real world nukes use X-rays. NIF is even located within LLNL, where about all modern american nuclear weapons are designed ffs. Straight from wikipedia headline:

It supports nuclear weapon maintenance and design by studying the behavior of matter under the conditions found within nuclear explosions.[3]

Same for Z-machine:

Since its refurbishment in October 1996[2] it has been used primarily as an inertial confinement fusion (ICF) research facility. Operated by Sandia National Laboratories in Albuquerque, New Mexico, it gathers data to aid in computer modeling of nuclear weapons and eventual fusion pulsed power plants.

The Z machine's origins can be traced to the Department of Energy needing to replicate the fusion reactions of a thermonuclear bomb in a lab environment to better understand the physics involved.

Fusion power, especially pulsed approach, is and always will remain a pipe dream and nice, palatable cover for general public, to be believed in by wide-eyed idealists and people who confused B-class sci-fi with documentaries. The value of collecting all that critical data for simulations, is just too great, and it's something that you can't obtain in any other way. Well, at least if you want to have functional diplomacy.

And it's not like that I'm against development of nuclear weapons, I'd just appreciate some clarity and honesty in this topic