Is there any way to make Dolphin’s thumbnailer ignore EXIF thumbnails for jpegs and always generate them based on the image itself? I believe the setting used to exist in earlier versions but I can’t find it anymore.
EXIF thumbnails can be blurry, flipped or just wrong. Example: save this image and look at it in Dolphin.
Hey @drinktheocean I found a possible solution just now.
Let me to explain what I do but I’m not sure what I do exactly but is in this actions lol…
First I read about Dolphin Arch Wiki
According to it I see package name kdegraphics-thumbnailers
so I try to install with yay, git version, but this process broke most of kde components and isn’t safe and I revert to install standard non git package but I leave only lib called 
libkdcraw-git v22.12.0.r2.g79b80f6-1
libkexiv2-git 22.12.2.r0.g9253280-1
as result of previous yay compiling task, you can install one by one by type in terminal ;
yay packagename
At this point you are installed theoretically 3 packages, so go on Dolphin settings (Ctrl+Shift+,) and to General>Preview untick (yes deselect) JPEG Image, then save.
Next I do re-login to session, but before open Dolphin I do cleaning of thumbs cache, to do so installing bleachbit and go trough simple app steps to performing cleaning.
when cleaning is completed I do another re-login, open Dolphin and ta -daah! LOL 
Boy that looks… impractical, haha
I found a workaround for this, just delete the EXIF thumbnails with exiv2 (thanks to winnie at Manjaro Forum for the advice). This simply removes said thumbnail without altering the image itself.
This is a one-way operation! File(s) will be permanently modified so backing up your data is recommended!
Delete exif thumbnail from a single jpg:
exiv2 -d t file.jpg
Delete exif thumbnail from every jpg in the current directory:
exiv2 -d t *.jpg
Clearing the thumbnail cache wasn’t necessary for me, it takes effect immediately.