From what I understand and verified in my testing is that the recompress original jpg quality setting will resample the image no matter what if it is set below 100.
max image size kb is what will trigger a resample if it’s over this size, even with the above setting at 100. Both of these happen server side.
composer media optimization image enabled happens client side and will resample an image before it’s even uploaded. I turned this setting off because it strips the metadata, it might be doing some resampling in your case too.