In the gitk preferences, I can select the “external diff tool”. It currently simply reads “meld”.
But meld is not my git-configured diff tool. That is set to Beyond Compare (for this project).

I have tried setting the “external diff tool” in gitk to empty. I just get an error box “: command failed: not found in PATH”.

It’s not really my goal to set any particular diff tool in gitk.
I am asking if gitk can be configured to fall back on the git config to work out the tool to use. Whether that be Meld, Beyond Compare or other.