Comment 11 for bug 1866565

Work around to start gedit again, if broken from missing schema key:

install dconf (ow-level configuration system):
>> sudo apt update
>> sudo apt install dconf

start dconf:
>> dconf

Navigate to key:
org.gnome.gedit.plugins.active-plugins

and activate the default values:
['filebrowser', 'spell', 'modelines', 'time', 'docinfo']

or eliminate terminal in your actual values:

=> gedit will start again.

PS:
I miss old style config files :-(