Just to clarify: remote I/O errors are expected when the program starts. After starting, clean the Bela console to get rid of startup errors (cmd K or ctrl K), then run the following from Supercollider on your host (it assumes the screen is connected to mux channel 1 as before):
~displayOSC = NetAddr.new("bela.local", 7562);
~displayOSC.sendMsg('/targetMode', 2); // stateful mode: target display can be set with: /target
~displayOSC.sendMsg('/target', 1); // change `1` to whatever multiplexer channel the display is connected
~displayOSC.sendMsg('/osc-test');
does "OSC TEST SUCCESS!" appear on the OLED? If not, can you post here anything that gets printed on the Bela console?