I'm assuming your "off label" use of Actemra is for PMR since it isn't FDA approved for PMR. There is no guarantee that Actemra will work for everyone with PMR. The SEMAPHORE study reports 49% of patients in the Actemra group no longer needed Prednisone.
https://www.medpagetoday.com/rheumatology/generalrheumatology/100815#:~:text=About%20half%20of%20patients%20with,Brest%2C%20France%2C%20and%20colleagues.
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I was lucky to have tried Actemra for PMR. I was able to taper off Prednisone after about a year. Actemra takes about 3 months to be fully effective. I was able to taper from 10 mg to 3 mg of prednisone in 4 months. I had to stay on 3 mg for another 6 months because of secondary adrenal insufficiency which was a side effect from taking Prednisone for 12 years to treat PMR. Adrenal insufficiency could be one reason why Actemra isn't allowing you to taper off Prednisone.

After I tapered off prednisone I had a flare of another autoimmune disorder and needed to take Prednisone again. Having other conditions in addition to PMR may be another reason why you can't taper off Prednisone.

It is possible that you were misdiagnosed and you don't have PMR.

Maybe you do have PMR but Actemra doesn't work for you since IL-6 isn't your primary inflammation pathway.

Remember that half the people with PMR who were trialed on Actemra weren't able to taper off Prednisone. If you aren't able to taper off Prednisone ... have you been able to reduce your Prednisone dose substantially?

I have been Prednisone free for 4 years. Actemra has been extremely effective for me.