Have you actually been diagnosed by a competent consultant or You are just feeling symptoms? Looking at your picture, you are still young to be facing bone loss. That said osteopenia is bone density loss. Have you got a confirmation after taking a DEXA scan? Osteopenia, osteroposis is no joke, I have seen family loosing muscle mass and bone density caused by cancer treatment. No one want to shrink later on in life.
BTW, I have no apprehension at this point and looking at my mother, I am hopeful


So, I am afraid I have success story to share with regard to that.
To fight osteopenia, you need to build, recruit muscles. You need to build back muscles. lumbar, spine and the entire core.
Full Posterior chain need looking after. your entire back, neck, rear dealt, lat, glute ( Yes glute is part of your posterior chain and is very important). Your core support your spine. I would work core separately mainly standing with weight. Many rotations and unilateral exercises. Check any imbalance and fix it. Work all type of strength ---- STS original and STS 2.0. For cardio do some plyo if you can. Plyo is good for bone density. It helps to strengthen glute too. Looking at it you need overall muscle recruitment. Latissimus and leg muscles are among the largest. The upper part of your leg is part of your core. If you have never tried body part from STS 2.0, try and see how your body respond. HTH.