It's called a SKLZ Lightning Bolt. You can find it here on Amazon. You can adjust the height of the trajectory, but the balls come out at different speeds and such so it's never really the same each time. I find it very useful. As you can see from the thread above there's a lot of debate on whether or not it helps to wear the glove/blocker. I do it barehanded and so far so good.
I use this and I know many goalies have in the past as well. It's essentially a baseball pitching machine you can safely use at home. Shoots small yellow HD foam balls (it's not that hard or soft) and meant for baseball practice. It doesn't pitch randomly, but sometimes the quality of the ball itself will cause it to shoot the ball faster or slower. It plugs in to the wall or you can pop some batteries in there to make it portable.
Long ago, I used to just throw a tennis or squash ball at a stationary yoga ball which would cause it to bounce back more unpredictably. Or I would throw a ball off the corner of the wall (so bounces off both walls) to mimic a deflection.
I bought the machine and the extra bucket of balls off of Amazon. I think when it was all said and done with shipping and tax it was like $140 CAD. Good deal for killing boredom during quarantine. I bought it when things were still really locked down. Here's the the Amazon link. I highly recommend the extra bucket of balls. Th machine only comes with 12.