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, you should check the APN to make sure it is turned on. There have been instances where the APN does not stay turned on after a restart.