Most effective home exercise for reducing leaning foward while working and standing?

I’m not sure that any exercise can reduce a need to lean forward over something. There are many exercises to strengthen the back, and a good physio should help. You can also change the position of the ‘something’, eg to raise or lower the working surface, to stop the need to lean. And if the problem is ‘dowager’s hump’, which is an osteoporosis problem, there are exercises for this as well as medical treatments like calcium supplements. Have a look at all of them on the internet, and decide what is most appropriate for your problem.

This question is for a physical therapist. Have your loved one or yourself evaluated by a therapist. This question can’t be answered here properly.