from https://arstechnica.com/gadgets/2025/07/a-mess-of-its-own-ma...

  Pixel 4a units contained one of two different batteries, and only the one manufactured by a company called Lishen was downgraded. For the Pixel 6a, Google has decreed that the battery limits will be imposed when the cells hit 400 charge cycles. Beyond that, the risk of fire becomes too great—there have been reports of Pixel 6a phones bursting into flames.

Perhaps your Pixel 4a had a non-Lishen battery? But if Google degraded your battery perf as well, then I have no idea.