Currently it only shows the lines that are different. Is there any way to make it visualize per-character difference inside those lines, same way as it does in Github here or in gitk in "color words" mode? https://github.com/microsoft/dotnet/pull/1282/files/cadcf3de421c9eabc1eb2f538bf26d9be3c65a91
UPD this question is NOT about gitk, read the title
This is the best answer I've found (in fact I'm turning it on now for myself!) https://stackoverflow.com/a/58405511/1007707
It is only for command line (I checked it doesn't affect git-gui), so probably not as helpful for git-gui.
Basically follow the instructions that come with recent GIT packages, on my system in /usr/share/doc/git/contrib/diff-highlight/README
Also, git-gui is a little dated, you may want to try another tool like git-cola or similar?