I followed this article to enable DNS Over HTTPS on the router-level. The problem is that it requires installing a package named "stubby" from a remote repository.
When upgrading OpenWrt, even though I checked restoring configurations, it seems that the packages are not restored. So, basically, the Internet connection does not work after upgrading OpenWrt, because the restored configuration relies on "stubby", yet it does not exist, and I cannot install "stubby" from the Web UI, because the Internet is not working. I had to do some cumbersome things like resetting the settings, installing "stubby", and then restoring the settings.
But, is there anyway to install "stubby" offline, like copying the package to another storage before updating OpenWRT, and then copy it back to OpenWRT using SSH, without requiring an Internet connection?