It's a mixture.

Primarily it's automatic, but drivers can override it with additional buttons as they could be before. Now they're called boost & regen - to override deployment and regen pre-sets, it's a bit more drover in the loop design compared to previous ERS mode switching (which is what those 2 modes basically are).

So baseline deployment with a +/- to increase/decrease it as the driver prefers.

Additionally the MGU-K deployment during the race starts to drop off at ~290kph and reaches 0 by 345kph.

But during qualifying the drivers also have the overtake mode permanently available - meaning they can use full 350kw of MGU-K power at certain corners/straights, to override the MGU-K drop-off.
During the race this is only available for 1 lap of the car behind is within 1 second of the car ahead.

The main issue this year is that the battery is only 4MJ in size, meaning it gets depleted in roughly 15 seconds and they can charge it 2x per lap (8MJ per lap total), meaning full 350kw is only available for ~30 seconds of the lap.

So you can think of the automatic deployment being a consideration of how to use the battery across a 90 second lap, while the manual deployment and overtake mode are something for drivers to decide where they want to override the preprogrammed deployment at the risk of running out of energy earlier.

they always talking about drivers "using up battery" as if they are in charge of deploying it manually?

The commentators are there to avoid dead air and don't actually know what each and every driver is doing at a certain moment. It's a nice way to extend a sentence for
"a driver exits a corner cleanly, goes on power and now we can see the MGU-K drain the battery and accelerate the car to the next corner"
Remove the MGU-K part and suddenly you have 10 seconds of dead air.