Install dconf and try the command below
dconf dump / > dconf.backup
If it doesn’t work, try with -f flag. If you only want gnome related settings try this
dconf dump /org/gnome > gnome-backup
If you use custom theme and icon, backup those separately.
Restore
- Full restore
dconf load / < dconf.backup - Gnome only restore
dconf load /org/gnome < gnome-backup