I get This site can’t be reached
Check if there is a typo in store.usps.com.
If spelling is correct, try running Windows Network Diagnostics.
DNS_PROBE_FINISHED_NXDOMAIN on various parts of USPS website, especially for informed delivery when AGH is enabled?
This isn't a topic for the GL forum.
You need to adjust your AdGuard Home filter lists and create exceptions.
But I never had the issue until the lastest 4.7 beta for MT6000.
It's not an issue with the router itself if it works when AGH is disabled.
Check which domain gets blocked and unblock it.
Have a look Adguard home query log that you visited the website. Could be blocked by your upstream DNS outside Adguard home.