Hi,
There are many possible causes that some terminals cannot detect Wi-Fi signals.
Common causes:
1. The Wi-Fi signal is weak.
2. The terminal is incompatible with the 802.11 protocol used by the AP/router, for example, 802.11ax (WiFi6) used by the AP, but the terminal does not support the 802.11ax protocol. Or the terminal doesn't support the frequency band /channel configured by the AP.
3. A security policy mechanism for a radio frequency signal, such as WEP, WPA/WPA2, and WAPI, may be set on the AP/router. In this case, if the terminal does not support the security policy, the signal transmitted by the AP cannot be parsed.