Update issue while updating macOS from Monterey 12.5 to 12.6

Have you uninstall Both VPNs

1 - [Not Loaded] NordVPNLauncher (App Store - installed 2022-04-03)

Modern Login Item

/Applications/NordVPN.app/Contents/Library/LoginItems/NordVPNLauncher.app

2 - [Not Loaded] LaunchHelper (App Store - installed 2022-09-13)

Modern Login Item

/Applications/VPN Proxy Master.app/Contents/Library/LoginItems/LaunchHelper.app

3 - Only for accuracy the computer is running macOS Monterey 12.5.1 (21G83)

4 - Worst case ----- >> is to Restart in Recovery Mode and choose to Reinstall macOS . It should pull down the Monterey 12.6 and commence the installation.

5 - Best and most reliable connection over Ethernet Cable to Router

Got it solved. In my case the cause was I had a poor WiFi signal so for any reason, the process of validating the upgrade image was timing out despite the image was already downloaded on my Mac. I connected the Mac to a Ethernet cable and the update process ran smooth:

Except for a tiny percentage of Macs, this update proceeds routinely. My employer has several thousand Macs and recently required all to update to 12.6. Most (like mine) went smoothly, the time remaining indicator was approximately correct, but some people reported that the update took "hours." Note that my employer requires an anti-virus package to be installed, plus some other things, and sometimes these updates take longer than "normal" because of those extra things.

First, did you allow it to proceed for a significant amount of time? Maybe ~ hours? Because you might have things installed that somehow are slowing down the update. Do you have any anti-virus, third party security tools, "cleaning" software, optimizers etc. installed? Make sure you have deleted any old 12.6 update/installer files. It might be helpful to get more troubleshooting inputs here by running Etrecheck with full disk access, post the results here with the Additional text button below. You can check before posting that the report contains no identifying info (it does not) but it will provide information on what is installed and the configuration that may help people here to assist in the diagnosis.

I was expecting ~ a few hours at most, not 24 hours!

Try this: create a new user with Administrator privileges. Try installing the update from that new user in Safe Mode. Make sure no leftover installers are in the Applications folder first.

If that still does not work, suggest that you boot into Recovery and run Disk First Aid. You can also reset SMC and NVRAM just in case something is hung there, but those are unlikely to help, yet no harm in trying them. (Instructions vary by Mac model, Apple has online instructions.) If still not working, download DriveDX to check physical health of the internal drive (how old is your Mac).

Finally, you can CONSIDER making at least two verified (through test restoring some folders and files) backups, preferably using different methods, such Time Machine and a "clone" utility like CCC or SuperDuper, then restore your Mac to factory settings, which entails erasing and reformatting the drive (hence the backups). Apple has instructions for doing this, they need to be carefully followed, the instructions are different for different models of laptops. Then create one new Administrator user with a name different from your previous users, say "Admin." Then apply all updates available, through 12.6. Then run Migration Assistant to migrate over only user accounts and files (no settings, no applications, nothing else) from your backup. Then install fresh only needed applications using up to date installers. This sounds somewhat involved but I have done it (due to a security update that could never complete on an older MacBook Air) and it is actually fairly straightforward, it takes an hour or two.

Alternatively, you could choose to stay with 12.5 if you wish to follow the mantra "first do no harm." Your Mac is working. But clearly something is not right because that is an update that should go routinely.

Perhaps others will see something ... the only thing I noticed was your VPN. Could that be impacting your connection to the Apple Servers?

I am in the same issue White_Lotus is. No matter how much time I wait, the update fails on validation. I'm trying to solve on my own... If I get any new, will post here.