Hey all, I haven't had any replies to my question on another site, so hopefully the official Zorin forum will yield some answers!
I've downloaded a few themes via https://www.gnome-look.org/, installed them all correctly etc. I go to Gnome Tweaks to selected them and they load fine. After about a minute however, Tweaks automatically resets my selections back to the default. I am completely at a loss here as I am completely new to Linux and I don't know what I should try, I also can't find anything specific to my issue online.
This falls down to a configuration issue and when there is more than one application managing the same configurations.
If a user installs Gnome Tweaks on Zorin OS while Zorin OS is still at all defaults, they will likely have no troubles setting the shell and system themes in the Tweaks Appearances tab.
But... IF there are already configurations existing in ~/.config for appearances and then new ones are set in Gnome Tweaks, which stores them in its own directory, it can create a Priority-read conflict as to which configuration to honor.
Your solution was to use Zorin Appearance, which by default saves the configuration in the correct Priority folder. Another solution might be to identify and remove the config file causing the conflict in ~/.config. As Zorin Settings also manages extensions; there really may not be much need to install Gnome Tweaks except for user preference in that app.