when we run the command
wo stack upgrade
It tries to run
apt install nginx-wo nginx-custom
and fails.
To find out why it cannot find the above packages, although the repos are added.
After more digging, I found out, there is a file blocking the updates/installs to these packages.
The file is: "/etc/apt/preferences.d/nginx-block"
So, I renamed the file to "/etc/apt/preferences.d/nginx-block.bak"
But after that, apt stops working, as it complains that the packages dependencies are broken. I tried 'apt install -f', it did not help.
I could remove the currently installed nginx-wo and nginx-custom packages, but that could have put the VPS into prolonged downtime of the sites in case the idea did not work.