Yes, still looks the same.
One thought of mine was to go into advanced Zorin settings when booting and choose an older version to go back. But since I am a Noob in this regard I am not sure if this will also change the boot loader again and my guess is actually NO
You mean selecting to boot an older kernel.
I can't see that will help change the grub menu formatting.
We need a grub mechanic here. Calling @Aravisian
yeah, that's what I meant
I could just install the Zorin Theme in the customizer from gnome-look.org
but this feels more like a visual fix than fixing the root/cause of the "problem".
I want to have it clean.
I'm clutching at straws:
Have you tried booting your ZorinOs bootable USB in "Try Zorin" mode, then come out and boot up normally?
EDIT: Just found this regarding Grub2 installing and re-installing. Grub2/Installing - Community Help Wiki
Scroll down to "Reinstalling GRUB 2" which I believe describes your situation.
"Try Zorin" mode is how I repaired the boot loader. But I didn't start the bootable usb a second time after that. I don't see how that can help?
But I have a new thought:
Would it be possible to delete (purge) the Ubuntu grub theme (if this even is a theme cause it seems Ubuntu doesn't care how their grub boot menu looks 
I guess the Zorin Grub boot theme was overwritten. Or should that still be around somewhere and if I delete the Ubuntu one (I don't know how it would work) then I would get the original from Zorin 16 again.
I will check your link, thanks
I have just found this:
I have never messed with grub myself, so I cannot guide you on this.
Hopefully @Aravisian may turn up.
So your link is super interesting and I even understand some things.
I didn't know what MBR in the menu of the Grub Customizer Program where it says "install in MBR". I still don't exactly understand it and what it would change if I did this in the Program.
The strange thing is (and what you said in the beginning): Grub is and always was on my drive although I installed it to the usb stick in the Ubuntu installation.
I though a Stick needs his own boot command/instructions cause it should be usable on any machine and start up the system on the stick...
Oh my head is exploding 
I have no clue what happend there.
I checked and I only have a Zorin folder in "Theme". It looks like this
inside like this
and the icons
That appearance is just a grub theme. Couldn't tell you if Grub Customizer or Grub Repair did the change but:
sudo nano /etc/default/grub
Arrow key to the bottom and add this line and remove any other GRUB_THEME line:
GRUB_THEME=/usr/share/grub/themes/zorin/theme.txt
ctrl+x to exit, y key to say yes, then enter key to save. Terminal will revert to normal. Then run
sudo update-grub
Mine looks exactly the same as yours.
I do not dual-boot on this desktop though.
Thanks a lot for the support!
Did exactly what you said - copy/paste
saved and updated grub.
But it didn't change anything when I restarted. Still the Ubuntu style Boot Menu.
Sorry, I just edited it because I forgot to change the line from my custom theme
GRUB_THEME=/usr/share/grub/themes/zorin/theme.txt
I don't get it. This is the exact same line. How does this change anything?
I tried it anyway. Well, nothing changed except for my brightness. My screen is glowing and I am not able to adjust the brightness anymore.
I can lower it but it doesn't affect anything - it shines like the sun.
I didn't do anything else but run your commands again and immediately restarted and boom - glowing screen
And what is that "nano" for in the first command?
sudo nano /etc/default/grub
And the only thing you did was trying to run Ubuntu Budgie, right?
It is so mysterious.
[edit]
I took a screenshot of Grub Customiser on my dual-boot laptop:
It is in Japanese but the items should locate in the same place in English version as well.
the only thing I did was trying to install Ubuntu Budgie on to my 32gb usb 3.0 stick. So I wrote everything needed on to that drive. Also the boot loader.
When I restarted I was able to choose all 3 OSs (Zorin, Windows and Ubuntu Budgie) from a Ubuntu boot menu. I chose Budgie to test it out. Restarted my computer after a while and was then stuck in the GNU GRUB 2.04 Command screen. With the stick and without it.
You might want to check the entry of your Grub Customiser and compare it with mine.
Basically mine is a dual-boot with Windows 11 and Zorin 15,3 and the boot screen is the one you want to have.
Mine looks exactly the same - apart from the Japanese 
And I thought your are French
I live in France but I was born in Japan 
Oh, wait.
You wrote the bootloader on that removable USB?
But you can still boot your system without that USB key?
Something does not mesh.
