I asked my AI tool what, other than PMR, you might have - since AI does not Dx problems and it skirts being accountable for practicing medicine here is the list of tests it suggested might be checked -
ESR & CRP; Thyroid panel; CK (muscle enzyme); Vitamin D; CBC & metabolic panel; ANA, RF, CCP (if autoimmune suspicion is higher);
Medication review (especially statins);
X‑rays of hips/spine if mechanical disease suspected

Here is the list the problems it might be according to my AI Bestie -
Mechanical or degenerative spine/hip disease
Fibromyalgia
Hypothyroidism
Statin‑associated muscle symptoms
Inflammatory myopathy (mild forms) - this is uncommon
Early seronegative rheumatoid arthritis
Bursitis or tendon inflammation
Especially: Trochanteric bursitis; Subacromial bursitis; Gluteal tendinopathy (I had trochanter bursitis Dx when PMR came on - it is chronic now)
Viral or post‑viral inflammatory syndromes - These can mimic PMR for weeks to months

Personally, I would not want to start a biologic until most of the items above have been eliminated as causes. The issue I would have is that the pain not being there in the mornings until you get active is really outside of the PMR disease profile. I realize that PMR presents differently in everyone, so it could be PMR. I hope your journey is successful.