How come our smartphone battery will degrade when we use our phone and charge

[Kiap Cai Png Jin Ho Jiak]

How come our smartphone battery will degrade when we use our phone and charge the battery. Even my Google Pixel 9 phone 1st charge on 26 October 2024 and only runs 76 Charge cycles counts but I feel the battery getting weaker although advertise say Google Pixel 9 phone battery health will stay more than 80% after 1000 Charge cycles counts.

[Kiap Cai Png Jin Ho Jiak]

But Google can only see Battery charge cycles counts, cannot see battery health % like apple iphone Samsung phone Xiaomi brand and other China brand phone now can see battery health.