Good morning, carmar.
Not sure if I had Synaptic Package Manager, but just installed it with the order you showed me.
After that, I searched for “zorin-appearance” into it, and it showed me this:
I did right-click and saw the “Mk for Reinstallation” option, but it is grey and I cannot click on it (not available), I don’t know why. The only available options are uninstall.
@Aravisian I’m running Zorin OS 15 Ultimate (that’s the license I bought a while ago).
What happens if you install Nautilus from terminal?
sudo apt-get install nautilus
Also shemas from terminal?
sudo apt-get install gsettings-desktop-schemas
If no luck there, try
glib-compile-schemas /usr/share/glib-2.0/schemas/
I just ran both, 0 installed or updated.
Same message when I run “zorin-appearance” --version:
(zorin-appearance:56667): GLib-GIO-ERROR **: 10:37:28.364: Settings schema ‘org.gnome.nautilus.desktop’ is not installed
«trap» para punto de parada/seguimiento
I just edited in an after-thought that I will repost here: 
glib-compile-schemas /usr/share/glib-2.0/schemas/
OK, @Aravisian.
I just ran the last one you edited. Result:
hector@DREAMS-PC:~$ glib-compile-schemas /usr/share/glib-2.0/schemas/
No such key “notify-with-tray” in schema “org.gnome.evolution.calendar” as specified in override file “/usr/share/glib-2.0/schemas/25_zorin-os-default-settings.gschema.override”; ignoring override for this key.
No such key “enable-hot-corners” in schema “org.gnome.shell:zorin” as specified in override file “/usr/share/glib-2.0/schemas/50_zorin-desktop-session.gschema.override”; ignoring override for this key.
Falló al crear el archivo «/usr/share/glib-2.0/schemas/gschemas.compiled.2CL2R0»: Permiso denegado
You may have something in your ~/.local/share/ directory that is overriding your /usr/share/glib-2.0/ directory.
You can test this by renaming the directory to ~/.local-bkp and rebooting. Test if Zorin Appearance is working.
If it is, then it may be necessary to sort through your .local-bkp directory to transfer over any user data you wish to keep that was not affecting this issue.
If it does not work, then remove the replacment ~/.local directory that was formed after your reboot and rename the ~/.local-bkp back to ~/.local - at which point: This may be a schema syntax error. If so, I am uncertain how to proceed. The Zorin Team may know the proper fix on that. As you chose Zorin Ultimate, you also have the ability to us ethe Contact form that comes with it.
And we can shoot them a message from this forum - keep in mind, it may take some time for them to see and record the response.
I tried that @Aravisian, but Zorin Appearance is still not working.
I ran “zorin-appearance --version” and same error.
How I contact the Zorin team then?
@ [artesan0]
or try PM to AZorin on here. 
Thank you so much, I just sent them a message.
Let’s see the solution, I’ll try to remember to share it here with you.
Thank you all!!!
Not trying to necro, but I am having the EXACT same issues!
Did you get a resolution? I just updated today from 15, and it went from being the gorgeous Zorin I loved to an ugly hunk of junk that has almost 0 features that existed before. Windows button doesn't work to open the menu, can't type in the applications window to find one I want either. But I just wonder if it is tied to the Zorin Appearance app not working.
iknowyerbad, did you accept a Direct Upgrade to "20.04"? Because if so, it installed Ubuntu 20.04 on your machine, not Zorin OS. Zorin OS 16 is based on Ubuntu 20.04, but any upgrades for it will be called to Zorin 16.
I have used Ubuntu 20.04 side by side with Zorin OS 16 and ... I can certainly understand the discontent at finding Ubuntu 20.04 on your machine instead.
Currently, the Zorin OS Direct Upgrade Option is not available.
In order to use the Direct Upgrade option, a release file within Root must be changed. Did you install Zorin OS on your machine or did it come installed with the machine?
Lastly, if your machine now has Ubuntu 20.04 on it; Sadly, the only thing you can do at this point is Re-Install Zorin OS. Please be sure to back up all of your important files.
I made a thread not long ago about [HOW TO] make an easier time of reinstalling Zorin OS, but since your case may be different (Your sources.list changed to different repositories), it may not apply in your case.
Have you previously upgraded, you use BleachBit?
Were you going to post a link to your [HOW TO] thread, or did you decided it was not appropriate in this case?
Yes, I wanted to avoid creating confusion. I figured I would mention it and if the poster wants to know more, they'll ask.
EDIT IN: Also, to both OP's above, do you use a Third Party updater app other than Software & Updates or Software Updater than what comes with Zorin OS? Might help narrow down the cause. Thanks to Zaba for bringing that possibility to light.
Hey @artesan0 , did you fixed your problem? I'm with the same error, but I don't have the paid version of Zorin.
Hey @Aravisian,
I installed the 20.04 Ubuntu update and I want to know if with this OS I'll be notified with the upcoming Zorin OS 16 update. Do you know if this is going to happen?
Are you saying that you performed the Direct-Uprade (Do-release-Upgrade)?
Ok, I'm only posting here because i encountered this issue & resolved it yt upgrading pip3
$ /usr/bin/python3 -m pip install --upgrade pip
$ pip3 install setuptools --upgrade
This solved my problem, that's all
type this in terminal and then restart
if you have lite edition
sudo apt install --reinstall zorin-os-lite-desktop
and
if you have core edition
sudo apt install --reinstall zorin-os-desktop
this work with pro and education editions too...
Marked Solution. 399