To build or restore muscle and bone tissue requires hard work - intense effort.
No amount of easy, fluffy stuff is going to cause positive tissue remodeling, or as the industry puts it, "make you look better naked."
It doesn't matter what you believe or what you think will do the trick. Your opinions on the issue do not supersede science.
In other words, you're thrice weekly tennis game isn't going to preserve or build muscle. Neither will your Yoga class or your morning speed walks with Mabel or your jog around the whatever it is you jog around.
So when you hear the industry experts say fluff like "Do what you will enjoy! Do what you will stick with!" ignore them. It's a good recommendation when trying to figure out a hobby, but not for transforming and strengthening your body. Imagine if that same expert said that about diet? Just eat what you enjoy! Uh huh.
You have to strength train and you have to do it properly, meaning, safely and with a high enough degree of effort that your body gets the idea that you want more of what you already have. Then you rest, meaning, take days off from exercise, and this is when you build and strengthen.
The little dude at the top of this post is lifting his barbell way too fast. He'd get an earful from me if I was training him.
When you lift, count a minimum of 5 real seconds to lift a weight and the same or slower to lower. Lift and lower until you can't lift the weight against your best effort to do so. Choose a weight or a resistance level that allows for between 60-90 seconds of total effort until your muscles are pooped out. Add a small amount of weight each session - as little as one pound. 5-10 different exercises are plenty.Train your whole body each session. 2 sessions a week. Let me know how it goes.