If it compiles when I press run …

Folks come to expect that if I press run and the code compiles that when I press build it will still compile.
And realistically why shouldn’t it ?
Run builds an actual application and, for the most part, the only difference was that now in a Xojo debug run the debug app has a bit of code in it for the IDE to talk to and control and query back and forth.

Other than that its “the same”

Except now.

With the addition of Workers what can happen is you can write code that, when you RUN, uses threads. And that means that certain code will appear to compile – although it might not do anything useful.

But when you BUILD now the IDE will compile that worker in to a separate console application.

Which means that your code that worked while you hit run all the time might no longer work. Or even compile.

I submitted this bug report about it Oct 10, 2020