There already is an alternate medication available for PMR patients.

Kevzara (Sarilumab) was recently FDA approved and currently is available in the USA for the treatment of PMR. Kevzara is an IL-6 receptor blocker just like Actemra. Kevzara studies were promising for PMR just like Actemra was for GCA.
https://www.news.sanofi.us/2023-03-01-Kevzara-R-sarilumab-approved-by-FDA-as-first-and-only-biologic-indicated-for-patients-with-polymyalgia-rheumatica
Kevzara probably won't be available in the UK anytime soon. Prednisone is still the only option and the best option in the UK. I was told my experience with Actemra to treat PMR wasn't relevant to the good people in the UK who have PMR only.