AT&T offers two very different products: rapidly expanding symmetric fibre (up to 5 Gbps) and legacy DSL still serving rural areas. Speed test results between the two are not comparable.
Enable IP Passthrough and add your own Wi-Fi 6 router. The stock gateway is the bottleneck on plans above 500 Mbps.
Almost always corroded contacts at the demarcation point. Ask AT&T to dispatch a tech and re-terminate the pair.
You need a 2.5/5/10 GbE NIC and CAT6 patch cables. Single-port laptops will always cap at 1 Gbps regardless of plan.