Battery health dropping so fast

That is totally normal. The battery health does not drop at regular intervals and you may see sudden drops and longer stretches of time when it does not drop at all. Replacement of the battery will be needed when it drops below 80% and that is usually after 3-5 years depending on full charge cycles.

All you can do is make sure the Optimized Charging feature is turned on. This prevents your phone from being at a 100% charge for long periods of time. You cannot overcharge your battery, but it will perform better if it is not always at 100% or at 0% for long periods of time. Optimized Charging learns you charging patterns and will charge quickly to 80%, then before you normally take it off the charger it will charge to the full 100%.

It's fine. Over longer periods, the Battery Health will decline an average of about 1% a month.

So, if your phone is 8 months old, you could expect the Battery Health to be about 92-93% at this time.

When the battery is down to 80% in another 12-18 months, it will be time to replace the battery.