Heavy arms

Well Covid19 affected all of my body, including my upper arms, so it could be a reaction to the jab. I would speak to a doctor though as it could be something else. Is it just the upper arms, or is the actual shoulder joints as well?

I had this type of problem when I started statin therapy. My medical notes now carry a warning that I am statin allergic since I tried most of them in quick succession. The most likely cause I can think of is a cervical problem i.e. a neck problem especially if it is both arms. Maybe posture related,. Try manipulation or perhaps a visit to a chiropractor?

Not seen it reported as being diabetes-related.

you need to see a doctor. There are many non diabetes related things it could be, such as double frozen shoulder.
We can't diagnose on here

Definitely see your GP. I suffer from shoulder problems when my vitamin D levels drop to the floor. Frozen shoulders are always the first symptom for me. But, it can be a symptom of many things.