There are available source codes for clients for all platforms (ESP32, ESP8266, Arduino with Ethernet module): https://arduino.php5.sk/opc-ua-esp8266.php?lang=en

Codes for OPC UA webservers for all platforms (ESP32, ESP8266, Arduino) are not available for free. If you want to buy them, contact me for more informations, payment method: martinius96@gmail.com