The fine was for not giving notice. They have implemented the same battery saving update on several more devices without any objection from the regulators because they gave notice for those.
European fines are entirely cope, it doesn’t mean they’ve actually done anything. Similarly laws like the GDPR and DMA aren’t made with the intent of being followed, just with the hope they’ll get fines or lead to the breakup of foreign tech companies.
There was no slowdown of devices; what happened is the devices didn’t randomly turn off anymore.