I could always open raw files, specifically Sony's ARW files with Gwenview without any problems. Then the update to 21.08.0 came by and I get an error message from Gwenview when trying to open an ARW.
This is probably some KDE package vs Gwenview issue (maybe Arch related) as Geeqie/showfoto/photoqt are working perfectly fine. I have downgraded gwenview but that didnt help. Gwenview is not plasma developers priority, so i advice you to use something else as this gets fixed https://bugs.kde.org/show_bug.cgi?id=441189
*** This bug has been marked as a duplicate of bug 441018 ***