Zorin Provides it's own desktop that only runs on Ubuntu 20.04 and Below. You can Change Everything, The Procedure is Same for Every Ubuntu Distribution. While you are using gnome (core) version. The procedure might be a little different. Also, You need to keep the version Of Zorin in mind cause a lot of themes are only made for Ubuntu 22.04 and Do not work on Zorin OS.
Take a Look at this,
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If Windows does not appear in the grub menu try the following command first. sudo update grub
Another way to resolve windows boot problems is with boot repair. sudo apt install boot-repair
The grub-customizer may allow you to add a windows boot entry if it can see it.
Grub-customizer will permanently change your grub configuration file which is difficult to restore if the package is removed.
I DO NOT recommend using Grub-Customizer in order to customize grub.
It can save configurations in unusual locations, making it difficult and frustrating to undo the changes.
It can also conflict with existing configurations, causing any number of headaches.
That being said... Yes, you can create a third party or user-made custom Grub Theme.
I do it, myself.
And Zorin comes with a Grub Theme that is made by ZorinGroup. You can even simply modify the Zorin Grub theme to your liking.
sudo nano /etc/default/grub
Look at the very bottom of the file and you will see if a theme is in use, what theme it is and the location it is stored in. In my case:
# Uncomment to get a beep at grub start
#GRUB_INIT_TUNE="480 440 1"
Zorin users that have not changed their grub theme should see the default Zorin Grub theme in its location.
A grub theme needs to carry its own Icons (for example, if you are looking to have a Custom Icon for Zorin OS and Windows), Fonts and a theme.txt file to tell it what to do.
You can look up guides on creating your own grub theme or download one you like from plng.com
I would say similar, yes. The overall appearance looks a slightly different color. But that image you posted matches the Zorin OS grub menu very closely.
Part of why I increased my grub menu size, changed the icons and background image and the fonts...
I do not recommend using Grub Customizer software.
But as an oldie or a newbie, you can explore customizing your system all you want and I encourage that.
Just... make sure you keep backups.
And with you having your disk fully encrypted CIA style... I would suggest using a practice machine for any changes and then applying them to your encrypted one once you have your technique really nailed down.