Ubuntu - how do I update "gimptool-2.0"?

[Ofnuts]

Code:

➤>type gimptool
gimptool is /usr/bin/gimptool
➤>realpath /usr/bin/gimptool
/usr/bin/gimptool-2.0
➤>dpkg -S /usr/bin/gimptool-2.0
libgimp2.0-dev: /usr/bin/gimptool-2.0

So you have to update package libgimp2.0-dev. Which Gimp version did you install? Standard from Canonical? From PPA? Flatpak version? AppImage?

Note that updating libgimp2.0-dev should also give you the updated C headers that will define things such as GIMP_LAYER_MODE_NORMAL_LEGACY (new in Gimp 2.10). It is highly probable that gimptool itself didn't receive any code updates (it is mostly a wrapper to call GCC...).