I have tried to update my pixel 3a without success for another year. It says:
"An error occurred while checking the last update. The update system will try again soon."

Unable to resolve the host "releases.grapheneos.org". No address associated with the host name."

Anyone have the same problems as mine already?

I know it's not from internet or VPN because my pixel 4a works fine with internet and VPN. I wonder if it's because of the sim card or not

    Balokzx did you resolve this issue? If you haven't updated in that length of time you can try to update by sideloading the OTA from here:
    https://grapheneos.org/releases#sargo-stable

    It is also highly advisable for you to move on from the 3a, it is a legacy device and as Extended Support Releases are due to cease upon the release of Android 13.