You need to work on your starting position. It’s a fine position for a conventional deadlift, but that is not what you’re doing; it’s okay because that’s a very common mistake. This is a mobility issue most likely. It can be uncomfortable, but you need to sink your hips lower and keep your torso as upright as possible. Work on stretching your hip flexors, glutes, and hips every day.
Because your torso is flat and your hips are farther away from the bar than they should be, your center of gravity is a little too far back. This becomes evident when you begin your triple extension – simultaneously extending your feet, straightening your knees, and shifting your hips forward and upwards. This is the reason why you fall backwards on the first rep. A better starting position (center of gravity closer to the bar, and thus tightening your triple extension into more of a vertical plane) should help with this.
You are jumping off the floor which is another reason you fall backwards. If you watch good Oly lifters, their heels come off the ground because of their triple extension, but their toes only come a few millimeters off the ground. You have a few inches of air there, which tells me two things, one good and one bad: first, you are capable of doing much more weight if you’re able to jump off the ground while holding this. (That doesn’t mean you should add more weight yet lol.) Second, if you’re putting that much energy into getting your body off the floor, that is all just wasted energy that should be going into the bar. My recommendation to remedy this is straight arm clean pulls. This focus of this exercise (I’m sure it’s somewhere on YouTube) is to focus on triple extension. We don’t care how much weight you’re holding when you do this. It doesn’t matter. I recommend doing it with the bar. Start with the bar slightly below the knees right before your hinge point, and as you hinge, extend up on your toes (keep them on the floor for the purposes of this exercise) and straighten your knees.
This one is just me being picky: When I clean, and when I’m teaching others how to clean, I like to mix in power cleans. In the first rep, it doesn’t appear that you pull the weight very high. A few cues for this is to put your shoulder into your ear–a very exaggerated shrug. You also want to think about pulling your elbows through the ceiling. The exercise for this is clean pulls. These start the same way as straight arm clean pulls, except here, you are pulling the bar up to your nipples and then lowering it: DO NOT CLEAN IT. Just pull it up, focusing on triple extension with a HARD shrug and throwing your elbows into the ceiling.
It’s hard for me to see, but I think I saw a little movement on your heels during the descent into the bottom of your squat. If I saw what I think I did, that’s a problem. To ingrain the feeling of where you should be catching the bar, go into a deep squat while putting as much of your weight onto your heels as you can. Hold this position for a minute. Rest a minute. Do it two more times. Then hold the bar in your front rack position and hold it for 30-45 seconds, all the while focusing on keep your weight on your heels. Because of your Oly shoes, the heel is the most stable place for you to put your weight in the bottom of a squat. It’s okay to have your weight on the midfoot in the starting position, but generally, if you aren’t catching the weight on your heels, you’re catching it on your toes which is much less stable (you won’t be able to do as much weight) and can be unsafe.
Positives: Your rack position is beautiful. Very few beginners have a front rack position as good as yours.
You have olympic lifting shoes. This is a huge benefit for people who want to be good at Oly lifting. It makes the positions and movements much easier to execute.
Your squat mobility is very good. Just focus on keeping your heels on the floor.
SINK the hips.
Sit BACK on the heels.
Good luck bro. Post another update soon and tag me in it.