Check your Wi-Fi band and signal strength
Hold Option → click the Wi-Fi icon in the menu bar → see your band (2.4/5 GHz), RSSI signal strength, and channel.
In the router's admin panel, try switching Wi-Fi channels — for 2.4 GHz, use channels 1, 6, or 11 to avoid overlapping with neighbors. RSSI worse than −70 dBm? Distance or obstruction is the problem.