Where to start? 36M / 5’10” / 200lb

Getting divorced, at peak motivation right now to turn around from years of being sedentary. I’d like to lose about 35lb and get back to where I was in the military 12yr ago.

This post from the other day is pretty much my exact goal. https://www.reddit.com/r/WorkoutRoutines/s/CIaOMmrP07

I know the first priority here needs to be fixing my horrible diet but I’m not sure where to start on workouts. I’ll have a gym at my new apartment and I’m not opposed to running outside for cardio. Also never really lifted, only ever did the bodyweight-type stuff we had for PT. My back is also rather easily fucked due to some service-connected happenings so I always need to be careful there. Even when I was in the military, PT was always more of a chore than something I had any inherent interest in but I’m trying very hard this year to get a new outlook on my fitness and nutrition. Any advice appreciated!