Development tools for Zephyr on STM32Workbench for Zephyr: VS Code extension to set up, build, flash and debug Zephyr applications on STM32.Devicetree manager: browse, edit and visualize Zephyr devicetree, STM32CubeMX-like for Zephyr.
It turns out this is a problem with 32/64 bit versions of JRE. For some reason, I had the 32 bit version of JRE and this allowed the project to be created but caused the problems described. Installing JRE 64 bit removed the problem.