Following the trail to the real source of the 90% figure, this doesn’t appear to be a current statistic.
The success rate for the U.S.-designed Excalibur shells, for example, fell sharply over a period of months — to less than 10 percent hitting their targets — before Ukraine’s military abandoned them last year, according to the confidential Ukrainian assessments.
This also is only regarding GPS jamming, which isn’t the only method of navigation. I feel the article is exaggerating quite a bit. I have no doubt GPS jamming was quite effective a year ago, I also have no doubt the Ukrainians have adapted since then.