Do barbell OHP seated on the floor (no back support) then do the same with dumbells. It is really important to get that full extension, push the bar as high as possible every mm counts.
Decline diamond pushups, many slow reps and get full extension pushing your body as far from the floor as possible. Do the same but with your hands on a medicine ball. Close grip incline bench too, fully extend your arms AND shoulders.
These exercises and variations put more stress on the smaller muscles that lag behind which are very necessary for the OHP, (like the serratus) most people lack OHP strength due to weakness in those minor stabilizer muscles (causing power leakage in the kinetic chain) rather than bigger ones such as delts and chest.
That’s how I reached a 155 lbs OHP in just 13 months of lifting.