@ralf
from your description of your usage, I'd say that it's a bit early to affirm that there is a problem with the battery indicator. What I gathered of your post is that you bought a FP4 in december last year - so it's a used device with an unknown years of use (or abuse: it's well known that not using a li-ion battery carefully leads to signficantly reduced usable life), you used the phone for a few days then set it in a drawer and with the last update of UT 2 weeks ago flashed it again.
That's not enough to be confident that there is a problem in the software and not in the hardware IMO. Strange patterns of charge/discharge are usual for damaged batteries.
As of myself, I have a FP5 since I bought it new 8 months ago, used it every day, I can't confirm a marked change since 24.04-1.3. This phone was energy hungry before, particularly if every feature is on, and it's still the case, no more or less as far as I can tell.