No VSIX File from Yarn

I cloned this repo and ran `yarn` in the directory, but couldn't find a ./build-artifacts folder or .vsix file to load into VSCodium. I'll admit to being a bit of a noob, those should be generated in the directory, correct? Is there anything else I need to run before `yarn`? I tried using Install Extension from Location, which seemed to work, but the extension never activates.