In this case, not much.
Everything in Zorin OS is Open Source and configurable by the user. This includes everything that is in Zorin OS Pro.
For many users, the out of the box experience is what they seek.
For me, personally, I like to add, remove, configure, modify, tweak... Make my own stuff...
Some stuff most users cannot "quickly" do... But most users could do more than they realize. Or at least, do what they want to do if so motivated.
I would actually need to go look... I mean, it's not asked about very often and I do not know everything that is in Zorin OS, myself. Partly because I prefer and use Zorin OS Lite. So there is a lot of stuff in Core I may have not yet seen.
I will address this personally, because it is probably the best I can manage at this time of night.
I have tried out many distros. Some, I really like, including MX Linux, Antix, Debian, Kali, Gentoo... There are some I don't like, but I won't mention the names of because that would be mean to distros like Elementary OS.
Zorin beats most on Performance, except Antix. And Antix leaves much configuration to the user. I have used Zorin OS 16 side by side with Ubuntu 21.04 and Zorin OS 16 left 21.04 in the dust.
I enjoy creating my own stuff, modifying and changing things around. Many Zorin OS users, should they borrow my computer, would probably not even recognize it as Zorin OS at all, on the surface.
As a Base, Zorin OS is excellent. I have had far more luck and a much easier time meshing scripts, applications and configurations into Zorin OS than I do on other Distros. Partly, this is because some other distros take too much control in trying to be unique, leaving me to have to undo some of their work before I can proceed with mine. With Zorin, that is far less common. On occasion, I need to modify a file in /etc somwhere. No big deal. But try sidestepping MintSources some time and you will see what I mean about making changes being like pulling teeth on other distros.
I like that I can customize Grub on Zorin to my hearts content, unlike some distros that lock that in. And Ubuntu is one of the distros that tries to be unique, meaning that the ZorinGroup already undid some of that work - to my benefit.
But then there are those who are not like me at all - they like to push the power button and get right to their own work. No customizing, no configuration, no modifying - they want a clean out of the box experience. And Zorin OS delivers that. I respect it.
Over time, I have been one of the most loudmouthed critics of the ZorinGroup as well as singing the praises. They are not perfect and neither is Zorin OS (Or any distro), but Zorin OS's flexibility, solidity and stability keep me on this distro, in spite of a lot of hopping for options.
This is what stands out for me, with Zorin OS. Speed, performance, adaptable... It is not just the theme and...
I never use any of the Zorin Themes. I don't really like them. They are well made, just not my taste.