It means that producing gallium is going to require a significant amount of time. You can't just magically will mines, refineries, and supply chains into existence. This is going to take years to do. Meanwhile, since China has fully domestic supply chains right now, it's going to be Chinese companies dominating the global market while these alternative supply chains are built out for western companies.

I absolutely know that US is not capable of growing industry trivially. In fact, industry only accounts of around 11% of US GDP at this point. There is also no skilled labour needed to grow the industry. Here's just one example of that https://www.popsci.com/technology/stinger-missiles-raytheon-ukraine/

Meanwhile, as the chart very clearly shows, other countries produce negligible amounts of gallium. Ramping up production of that overnight isn't going to happen. The real point here is that gallium and germanium are just a couple of items where China is a bottleneck, and restricting their export is simply demonstration. There are plenty of other things China can cut going forward if US continues to play this game.