Hey chika,
Very hard to see your back from that angle but from what I could see it still looks like you are rounding your back more then I would like.
When you drop down to grip the bar, try this,
just bend over from your hips and reach for the bar and grab hold of it.
Then when you are ready to lift it
flatten your back and drop your hips lower, more so that the tops of your thighs are more nearly parallel to the floor.
(If you look at your vid you will see that your thighs are like at a 45° angle to the floor).
Remember to push the weight thru the floor and to push your pelvis forward with yor glutes.
This should help to flatten out your back.
We need to get this nipped as soon as we can cuz I know you wanna do big weights, you certianly have the strength to do it.
Best regards suga,