Have just installed version 4.0+(2020-06-27). Unable to print anything because it does not find my printers. Previous version - 3.10+(2020-04-11) - is fine. Running with MacOS 10.13.6.
Work-around: Edit /Applications/Gnucash.app/Contents/Resources/etc/gnucash/environment and add somewhere convenient GTK_EXE_PREFIX={GNC_HOME} I've pushed a change that will build that in from 4.1 on.
Thank you. Very simple - fixed!