As with the first patch, the update preallocates space for an entirely new copy of BG3 (~85GB), downloads the small patch, then does something along the lines of copying/moving large amounts of data, finishing up with deleting those 85GB it just preallocated.
For anyone still having troubles/has not yet downloaded the update, make sure you have at least 85GB of space. Alternatively, delete the game and do a fresh install.
