I have copied a Delphi 10.2 target and I am updating the copy to 10.3
In an “Embarcadero Resource Compiler” action, automatically changed with your updater to select “Compiler Version 10.3 Rio”, the action now looks for the exe referenced using %DELPHI_10_3_BRCC32%, which is not defined, so the action fails. In the project variables, the only relevant value name I can find defined is DELPHI10RIO_BRCC32 and points to cgrc.exe. I don’t know if this is your issue or EMB’s, but it works if I change this action back to Tokyo, which is still installed.
And one other small thing: it would have been good if the built-in upgrader to 10.3 Delphi had disabled the Fixpack/FastDCC option while doing so, since this is not available for 10.3.