I was told about 10 years ago to always get shots in your dominant arm.
Nurse said the pain goes away faster because you move it more. I thought “makes sense”.
My experience with flu shots since seems to confirm this. For many years at work and then the county, the assembly line always was set up for you to get jabbed in the left arm. The pain always lasted 3 or 4 days. Once I’ve turned around the pain in the right lasts 1 or 2 days. Covid shots hurt for 2 days, shingles was 3. fwiw