As I understand it the backend and all the app packages are open source, and the front end is developed openly too, but yes regrettably the front end isn’t open source itself any more.
re: cloudron, the license and context around re-licensing was a bit worrysome. Their packaging may be open source but if you dive into the details of it, it is completely tailored to their system. On first thoughts, that would make sense except when I realised that a lot of the app containers are built up from scratch - even when upstream projects release the containers ready-to-rip. They cite some docker security issues but again, it just compounds the fact that once you’re on cloudron, you are on cloudron and won’t easily be getting off of it.