I cannot get my RS485 MKR shield to communicate and I believe it is because the Wi-Fi module is using the Tx/ Rx pins (13, 14). I should have bought the MKR Zero since those pins are open on that version. I assume you can re-assign the serial pins so that is what I am looking into now.
the NINA only uses RX/TX for BLE (or fw update). try to initialize RS485 after WiFi.begin