Reason: Obviously, there is a member of a class renamed by espressif:
\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\3.1.2\libraries\ESP8266WiFi\src\WiFiServer.h
line 85 reads:
WiFiClient available(uint8_t* status = NULL) __attribute__((deprecated("Renamed to accept().")));

It can be fixed easily. Just edit file
\Documents\Arduino\libraries\RemoteXY\src\RemoteXYComm_WiFi.h
at line 95.
change it from
WiFiClient cl = server->available ();
to
WiFiClient cl = server->accept ();

Thank you.