Is there a way to change the default background color for all of the templates, the default value is #505050 (in dark mode) but I like want it to be a bit more darker, I can do this manually but it's a pain doing it for each new document, I see that in the preferences.xml file there's a value for this setting but everytime I change it the value resets to #505050.

Sundish

I see that in the preferences.xml file there's a value for this setting but everytime I change it the value resets to #505050

This should work as long as Inkscape is not running in the background when you edit preferences.xml. Also remove the setting from your user template (default.svg) if you saved a new one earlier from the menu in Inkscape.

Yes! that worked. Thank you.