Hi
Forge has changed how they serve their downloads, and that impacted availability in MineOS. There is a fix underway: [SOLUTION IN PROGRESS] Can't download forge profiles - #11 by jagdtigger
After installing MineOS you need to update the WebUI to get the latest commit: Updating the Webui - MineOS Wiki
This is beacuse the premade ISO’s do not nescestarily include the very latest updates and commits.