People have been recording brain activity for decades, but the scale is very different. Until about 10-15 years ago, most labs were using a handful of electrodes (my PhD work, for example, was done with 1-2 at a time). With cheaper amplifiers, it's become more common to use arrays with ~32-96 electrodes and they're often implanted chronically in the brain.

Neuropixels are fairly new and offer ~300 channels (selectable from ~1000). The neuralink thing would increase this another 10-fold.