!!! For M1/M2 apple silicon see this comment:
For MacOS | Mojave | High Sierra
brew upgrade gnupg
brew install pinentry-mac
echo "pinentry-program /usr/local/bin/pinentry-mac" >> ~/.gnupg/gpg-agent.conf
killall gpg-agent && gpg-agent --daemon
git config --global gpg.program gpg
git config --global commit.gpgsign true
Thanks! I use MacBookAir M1 Machine and the modified version of this guide from @shaunsim15 works for me.