I'm not sure if this is significant, but after install/restart of 2026052401 (i.e. with security preview releases) on a Pixel 8, I put the phone on recharge overnight. It successfully recharged to 80% (I have battery charging optimisation enabled). Next morning, after removing from charge and everyday usage (some time not in use, sometimes browsing, sometimes using other apps, etc) the reported battery charge did not shift AT ALL from 80%.
After several hours, when I had guestimated/anticipated that remaining charge would be about 70% (but it was still being reported as 80%) I restarted the phone. On restart, reported charge was 71%. Since then, battery charge has fallen, in a manner consistent with what I normally expect in use.
So what I observed did not persist past a second reboot. I report my observations here, in case it is a sign or side-effect of some other concern.
I have observed no other unexpected behaviours or concerns with this update.