Usually when doctors say there is nothing they can do for you, it means there's nothing more medically they can do within their specialty lane. However, there are other things that can help you manage your symptoms.

I did some poking around and came across this excerpt from Medscape on management of Corticosteroid-induced Myopathy:

{ "Some literature suggests that aerobic exercises and resistance training may help to prevent weakness or reduce its severity. Although there are no definitive recommendations regarding therapy for steroid myopathy, it would seem reasonable to direct therapy to address the weakness and resulting impaired mobility. Range-of-motion exercises (either passive, active-assisted, or active, depending on the degree of weakness) and stretching exercises should be performed to prevent joint contractures. As a general rule, resistance exercises should be limited to muscles with greater than antigravity strength. Bed mobility, balance activities, transfer training, and gait training should be included to address decreased mobility. However, high-intensity exercise should be avoided because, according to some preliminary animal research models, it may be harmful. Occupational therapy may focus on maximizing the patient's ability to independently perform activities of daily living." }

Also, here is a link to a PubMed article on Corticosteroid Induced Myopathy:
https://pubmed.ncbi.nlm.nih.gov/32491663/
Have you inquired with a physical therapist or occupational therapist who is is knowledgeable about muscle atrophy? Are you still needing to take steroids?