If you are a git user, you can install the theme and keep up to date by cloning the repo:
git clone https://github.com/dracula/gimp.git
Download using the GitHub .zip download option and unzip them.
cp -r ~/gimp/Dracula/ /Applications/GIMP-2.10/Contents/Resources/share/gimp/2.0/themes/
cp -r ~/gimp/Dracula/ ~/.config/GIMP/2.10/themes/
Preferences > Interface > Theme > Dracula : OK
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