Could You open the Terminal and type sudo apt update && sudo apt upgrade and show here the Output? In general I would say that it is good to set the Sources to Main Server and not to a regional Server. But it depends on the individual Situation.
barbod@Barbood-NoteBook:~$ sudo apt update && sudo apt upgrade
[sudo] password for barbod:
Get:1 http://security.ubuntu.com/ubuntu focal-security InRelease [114 kB]
Hit:2 http://archive.ubuntu.com/ubuntu focal InRelease
Hit:3 http://ir.archive.ubuntu.com/ubuntu focal-updates InRelease
Hit:4 http://ir.archive.ubuntu.com/ubuntu focal-backports InRelease
Hit:5 http://ppa.launchpad.net/zorinos/apps/ubuntu focal InRelease
Hit:6 https://pkg.cloudflareclient.com focal InRelease
Hit:7 http://ppa.launchpad.net/zorinos/drivers/ubuntu focal InRelease
Hit:8 http://ppa.launchpad.net/zorinos/patches/ubuntu focal InRelease
Get:9 http://ppa.launchpad.net/zorinos/stable/ubuntu focal InRelease [18.1 kB]
Hit:11 https://repo.steampowered.com/steam stable InRelease
Hit:12 https://packages.zorinos.com/stable focal InRelease
Ign:10 https://403.online/repos/code stable InRelease
Hit:13 https://packages.zorinos.com/patches focal InRelease
Get:14 https://apt.kitware.com/ubuntu focal InRelease [15.5 kB]
Hit:15 https://packages.zorinos.com/apps focal InRelease
Hit:17 https://packages.zorinos.com/drivers focal InRelease
Hit:18 https://packages.zorinos.com/premium focal InRelease
Err:14 https://apt.kitware.com/ubuntu focal InRelease
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 1A127079A92F09ED
Get:16 https://packages.microsoft.com/repos/code stable Release [3,065 B]
Get:19 https://packages.microsoft.com/repos/code stable Release.gpg [481 B]
Fetched 151 kB in 4s (36.2 kB/s)
Reading package lists... Done
Building dependency tree
Reading state information... Done
1 package can be upgraded. Run 'apt list --upgradable' to see it.
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://apt.kitware.com/ubuntu focal InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 1A127079A92F09ED
W: Failed to fetch https://apt.kitware.com/ubuntu/dists/focal/InRelease The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 1A127079A92F09ED
W: Some index files failed to download. They have been ignored, or old ones used instead.
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
The following packages were automatically installed and are no longer required:
adwaita-qt coinor-libcbc3 coinor-libcgl1 coinor-libclp1 coinor-libcoinmp1v5 coinor-libcoinutils3v5 coinor-libosi1v5 libfuse3-3 libnss3-tools libxmlsec1
libxmlsec1-nss
Use 'sudo apt autoremove' to remove them.
The following packages have been kept back:
xdg-desktop-portal
0 upgraded, 0 newly installed, 0 to remove and 1 not upgraded.
As far as I can see You have a Problem with that apt.kitware.com Repo (Entry 14). I don't know what this is for but when you don't need it anymore You should delete it and try it again. And you have an ignored One: Entry 10: 403.online.
I suspect either the ISP or Zorin OS has restricted access for Iranians using IP addresses or similar means. However, I'm unsure how to address the Bluetooth issue. Despite being mostly off, the panel consistently shows me to turn off Bluetooth. Occasionally, it operates smoothly. I attempted to resolve the matter using Blueman, but it didn't work
Zorin OS does not and will not restrict any of your sources or access.
You might check in Software & Updates > Other software and set "Download from:" to Main server
The sources show as set to the Iranian Regional Server, not Main Server.
