I know it's a ridiculous thing to say, but the fact that I can customise the font so well on the website only to then not be able to download it like that is a crime. I don't want to muck about with npm just to build a font - do it on the site! /rant
Well, I was able to do it fairly simply online via github actions with the help of chatgpt.
Chat history (excuse the lazily-constructed prompt): https://chatgpt.com/share/6acf829b-5428-83ec-939c-acbc7805a3...