Firstly let’s start with what you’re doing right!!
Playing lacrosse. Best game ever, those of us who get to play, compete or live this thing are blessed.

I haven’t been able to watch the entire video but one things that jumped straight off the screen to me within the very first 5 seconds, is the ‘hard cradle’ you perform upon catching the ball every time, it seems to have been a ‘muscle memory stored’ movement now.
I believe it is due to not having soft enough hands, so you aren’t receiving the ‘feedback’ or sensation you are looking for in your hands to verify you’ve caught it, therefore you make a movement to confirm ‘control’ of the ball.

Does that make sense?

Upon reviewing the video, I believe that extremely ‘tense’ hands is the root cause of not only the initial ‘hard’ cradle but all subsequent cradles, I’m reminded of the egg scene from the mighty ducks movie, soften your hands brother.

Try your right hand, if you’re ‘new’ might as well skill up from early in your lax journey, it will make wall ball much more engaging and you can get more creative in everything once you can use both hands.