this is a good clue and it means we don't need the video, and it means you can fix this.
when you originally described twisting on your hips when you lifted your left foot off the ground, I feared that you had lower back problems, which are notoriously complex and at 51-years-old they are best left alone. but what you have is a hip and thigh issue and that can be worked on.
the problem is essentially the opposite of what's called crossover gait, which is where folks place their foot plant too near, or even over, the midline of their running. you are doing the opposite, you turn your foot out and just like the crossover guys you can learn to not do this.
basically, your adductors are too weak and your abductors are too strong and the imbalance is twisting your leg out of line. it's a bit like a suspension bridge, the cables have to be properly tensioned to keep the bridge level and you need to work on tensioning the inner ones (adductors) and releasing the outer ones (abductors).
it takes time, and patience, but you can do this.
those bridges and lunges you've been doing are good, so keep that up.
the mini-band is a good training aid for these kinds of exercises so get one of those if you haven't already. it's just a big rubber band you loop around your ankles and then move your feet against the resistance of the band. you walk in different patterns like triangles and rectangles and do figure of eights and stuff and you feel daft and hope no one walks in while your doing it, but it works.
this is also a good exercise for hip flexors and quad stretch: stand with your feet close together, and parallel. step forward with one foot (we'll say the left) so that your right knee comes down to the ground. your left foot should come sufficiently far forward that both knees form right angles. hold that position for a second. place your hands on your hips, and ease your hips forwards, keeping your torso upright and erect. hold that position, and relax, then push again, and relax, and stand up. repeat with the other leg and do that 2 - 4 times per leg, per session.
once you feel that the core work and exercises are having an effect you need to start consciously thinking about foot plant as you run. concentrate on keeping your hips forward and your body upright and placing your foot quite deliberately on the ground with the toes facing to the front. you might need to do this very slowly at first, maybe even at walking speed, and you won't be able to keep it up for very long to start with but just gradually increase the time and distance of the thinking part of your run. I've had folks do this on a treadmill which they find helps because they don't have to worry about pace or looking out for pedestrians or whatever and they just focus absolutely on their posture and foot plant.
training works precisely because the body adapts to what you do, and it gets used to and comfortable with how you move, so when you change something the body squeals and complains and argues with you which is why you change stuff slowly, and gradually, and gently, and you persuade and cajole the body into the new you rather than battering it into submission. be gentle with your body and it will in turn be gentle with you.
good luck.