Any advice on where I’m going wrong with lumbar extension is appreciated
This is honestly a pretty rough angle to pick out mistakes with the deadlift. Deadlift issues tend to stem from set-up, and in this shot the plates are covering your feet and the bar in relation to your body. A front 3/4 shot from a normal standing height would be more effective.
From this shot, I don’t see anything too wrong. Maybe the bar is too close to your shins at the start, forcing your shoulders too far over the bar and causing your hips to rise early since they can’t get under your shoulders, but that’s very rough speculation from what I can see.
Fair enough, I’ll work on a better angle and make sure I’m not too close .