Do Helium, or any other browsers with intent to keep supporting MV2 extensions say what they intend to use as a repository to acquire them?
I don't think the chrome or microsoft extension websites even let you upload a MV2 extension anymore, and most chromium forks I've used rely entirely on the chrome web store.
FWIW, I think ublock is probably the most important mv2 and they've got a GitHub repo here that builds it automatically (not sure if the browser uses this, I just saw it and remembered this comment)
I don't think the chrome or microsoft extension websites even let you upload a MV2 extension anymore, and most chromium forks I've used rely entirely on the chrome web store.