With digikam 4 it was possible to adjust the timestamp of RAW files (at least Canon CR2, not sure about others), this fails with digikam 5. Trying to update any timestamp via the 'Time Adjust' tool in the BQM results in 'Failed to process item ...'.
Can you try with last digiKam 5.7.0 Linux AppImage just released ? https://www.digikam.org/download/
Just tried the 5.7.0 Linux AppImage, the behavior is still the same. For if others run into the same issue, exiftool can be used as a workaround: 'exiftool -alldates-=3 IMG_8117.CR2'
Did you turn on the Raw write mode in Setup/metadata panel ?
It's reproducible with 6.0.0, using stand alone Time Adjust tool restored by Maik for next 6.0.0-beta2 release. Please test with current bundles from https://files.kde.org/digikam/ All files will be updated today morning. Gilles Caulier
Tested with the latest git/master version. The writing of metadata in RAW files can be reactivated and Time Adjust tool exists again. I close the bug. Maik