DIAGNOSIS Your laptop is likely connected to the congested 2.4GHz band, or it lacks Wi-Fi 6 (802.11ax) capability, limiting speed. The symptom is high signal strength but low throughput.
FIX First, verify the connection. On the laptop, check which Wi-Fi network you are connected to. It should be your 5GHz network (SSID likely has '-5G' suffix). If connected to 2.4GHz, disconnect and manually select the 5GHz network. Second, check laptop capability. Search your laptop model's specs for 'Wi-Fi 6' or '802.11ax'. If it only has Wi-Fi 5 (802.11ac), maximum link speed will be ~866 Mbps under ideal conditions, not 1201 Mbps.
IF THAT DIDN'T WORK Log into the router. Go to Advanced > Wireless > Wireless Settings. For the 5GHz band, ensure the 'Enable WMM' box is checked. Go to Advanced > System Tools > System Parameters. Ensure 'NAT Boost' is enabled. These are hardware acceleration features required for full speed.
HEADS UP The AX21's 2.4GHz band max theoretical speed is 574 Mbps, but real-world speed in typical environments is 50-150 Mbps due to interference. The 5GHz band is essential for high speed. A Wi-Fi 5 client will not achieve the full 1201 Mbps PHY rate advertised for the AX21's 5GHz band. Speed tests should be done with a wired connection to isolate wireless as the cause.