This post https://gohugo.io/hugo-modules/use-modules/ on the Hugo site implies that using Hugo modules for themes is possible with Netlify, and (in my opinion) much tidier than git submodules.
But I cannot get it to work, the deploy just constantly fails, not finding the theme (I think this is true because I can see the build process is not finding a custom shortcode). The process works fine locally, and also works when I test with netlify dev locally.
Any ideas? Is there anything extra I need to do to get modules to work on Netlify?