Flatpak theming:
Seeing how the Zorin team added more theming options in Zorin Appearance (including a link for installing third-party themes), it would be beneficial if the guide included things from the following article:
It explains how to apply themes to Flatpaks installed from Software store via Terminal or GUI (Flatseal). I think the latter would be a better choice, considering Zorin is trying to be as beginner friendly as possible 
Zorin's GTK4 style:
Default Zorin themes need to be updated to properly apply on all parts of GTK4 applications. Installing Gnome's latest versions of apps and applying Zorin themes now results in some parts not being properly styled.
How it looks without Zorin theme applied:
How it looks with Zorin theme applied:
There may be other areas that also need updating, I only noticed these.
Adding these changes to Zorin would allow users to download the latest versions of Gnome software while also having a single application theme, making the desktop look more unified.