The boring answer, offered because it is right more often than any of the clever ones: give it a week of normal use, including a few nights on charge, before concluding anything.
Most of the settling work needs the phone plugged in and idle. If you have had three short nights since updating, the background work has barely run and you are measuring a phone mid-task.
A reasonable timeline:
- Days 1 to 3: expect it to be worse. Do not diagnose anything.
- Days 4 to 7: should be visibly improving. If it is, you are fine.
- Beyond a week with no improvement: now it is real, and the breakdown above will tell you which app.
One thing worth doing on day one that costs nothing: restart the phone. Not because it is magic, but because updates leave processes in odd states and a restart clears the ones that are stuck. It resolves a surprising share of post-update complaints and it is the first thing support would ask anyway.
And if you are on an older device, be honest about the alternative explanation: batteries lose capacity with age, and the update is often just when you started paying attention. The battery health figure is worth checking before blaming the software — if it has dropped a long way, no update is going to fix that.