I have a WPA2 Wi-Fi network and currently using self-signed certificates. My iOS devices request I accept them manually. My MacBook pro asks as well. My Android (Samsung), just connects. Is that normal? Kind of concerns me it doesn't even warn you.
While it is frustrating, keep in mind that ultimately a user is being asked to make a security decision. When most users are prompted in Windows, iOS and macOS, they're usually blindly accepting the certificate. Even if the user were to examine the certificate, there is nothing to compare against (unless IT has explicitly told all users what to look for).
If security is top of mind, tunneled EAP methods with password exchange should not be used. In environments where some devices are unmanaged, EAP-TLS is the only safe bet.
Note that Android 7.1 and higher has greatly improved EAP server certificate validation.