If it is this one that you mean: https://www.nejm.org/doi/full/10.1056/NEJMoa2027540?query=featured_home
Then doesn't do that. It monitors the parts of the brain that produce the speech not the parts that have the intent.
We implanted a subdural, high-density, multielectrode array over the area of the sensorimotor cortex that controls speech in a person with anarthria (the loss of the ability to articulate speech) and spastic quadriparesis caused by a brain-stem stroke.
Emphasis mine.
It is not monitoring thoughts but monitoring the part of the brain that articulates those thoughts.
The paper also says:
We decoded sentences from the participant’s cortical activity in real time at a median rate of 15.2 words per minute, with a median word error rate of 25.6%. In post hoc analyses, we detected 98% of the attempts by the participant to produce individual words, and we classified words with 47.1% accuracy using cortical signals that were stable throughout the 81-week study period.
So it's a long way from reading anyone's mind.