It seems like you can't use B4JPackager or the "Build Standalone Package" function to build a 32-bit version of apps. OpenJDK 11 is required and it is 64-bit only. I downloaded the OpenJDK 14 installer but that also is 64-bit only.
Can I build 32-bit standalone packages using these tools? I found a 32-bit version of OpenJDK 11 at Bell-sw.com, but I get "error: module not found: javafx.swt" when I try to compile my application.
Another option is to create a 64 bit package and also distribute the compiled jar for the few customers who still run 32 bit computers. They will need to make sure that Java 8 is installed.