gsettings set org.gnome.settings-daemon.plugins.xsettings overrides \
"{'Gtk/DialogsUseHeader': <0>, 'Gtk/ShellShowsAppMenu': <0>, \
'Gtk/DecorationLayout': <'close:menu,maximize'>}"
When trying this, a second issue occurred with this message: "GLib-GIO-Message: Using the 'memory' GSettings backend. Your settings will not be saved or shared with other applications." Turns out this is because Anaconda has usurped GSettings:
beli@Hex:~$ which gsettings
/home/beli/src/anaconda3/bin/gsettings
This is a bug, as is discussed in multiple Stackexchange post but this one had the best (cross-application) solution - simply execute the original gsettings executable: usr/bin/gsettings. And a third: Despite being in Blogger's Compose interface, I had to manually insert the <0> s because Blogger wasn't auto-substituting < and > around 0 with < and > as it's successfully doing elsewhere in the same line.