We have observed with Google Maintenance the following issues;
1) If there is a GigSky eSIM already installed on the phone, after the December 5th Android updates the APN has been removed. To re-add the eSIM, please see the Add eSIM document -https://support.gigsky.com/hc/en-us/articles/360039715994-Set-APN-settings-for-Google-Phones-Pixel-3-4-eSIM
2) If you're downloading an eSIM after the maintenance, the APN is not set. To set the APN, go to Settings and search for Access Point Names, then select the GigSky APN to be used.
3) After a restart of the Pixel phones, turn Roaming Off and On to ensure the APN is selected for use.