You write your iPhone was at 98% and it was 8 months old, and in a few weeks it went from 98 to 95%. There is nothing to worry about. The calculation of the battery's maximum capacity is not updated all the time, therefore a few percent may be taken suddenly at once. Apple recommends that the battery be replaced when it is at 80%, so you have lots of good time left with your current battery.
Just for comparison. A week or two ago I had 99% battery capacity on my iPhone, it is from November 2022 - the other day I checked again and it said 96%, (95.4%) after 157 full charges. I think it is very normal.
You can find more useful information here:
iPhone Battery and Performance - Apple Support