Hi @garryshortt ,
The tutorial Using PLC IDE With Arduino Cloud requires a version ⩾ v 1.0.4 of the PLC IDE & PLC IDE Tools. The tutorial will be compatible with upcoming releases of the software.
Regarding the message displayed in Arduino IDE, it is not an error message. The sketch was successfully uploaded as noticed. Please take a look at this article: https://support.arduino.cc/hc/en-us/articles/4411327110674-Warning-Invalid-DFU-suffix-signature.
To program the Opta in PLC IDE, it is necessary to download the Runtime and connect to the board as indicated in steps 3, 4 and 5 of the following tutorial: https://docs.arduino.cc/software/plc-ide/tutorials/plc-ide-setup-license/
As for the last point concerning the memory , you can consult the following tutorial:
https://docs.arduino.cc/tutorials/opta/memory-partitioning/.
Best,