Please check the following.
Are you too far away from the wireless access point?
Please move closer to the access point and search again.
Is the wireless access point encryption method "WPA (TKIP)" or "WPA2 (TKIP)"?
If your wireless access point isn't found by your Nintendo Switch despite being found by other devices, or if the wireless access point is found, but it's listed in grey and trying to select it leads to "This Network's Settings Are Not Supported", it's possible that one of the above encryption methods is being used.
These encryption methods are not supported by Nintendo Switch, so please use a different encryption method, for example, "WPA2 (AES)".
Is your access point configured as hidden?
Hidden access points* are not displayed in the list of found networks.
If you'd like to connect to a hidden access point, select "Manual Setup" on your Nintendo Switch and enter the necessary information. Networks configured via manual setup appear at the bottom of the list of found networks.