Immutable OSs are great, I'm running a custom image based on Bazzite for a couple of years now.

But that doesn't solve the user sandboxing problem, flatpaks and xdg portals does.

Still, a lot of portals are still missing or not fully implemented, but it's getting there !

At the end of the day, a sandbox is a slice/cgroup. i.e.: Kernel's ability to create a complete bubble around a process or set of processes.

My beef is not with immutable OSes or sandboxes or else. They all have use cases and reasons.

My primary beef is being locked out of my own system without my consent. I want to own my personal (esp. Linux) systems, that's all. I'm also against erosion of Free Software ecosystem for something looking open, yet non-buildable or modifiable by the end user. This is why I don't like permissive licenses and essential software to be licensed-washed from Free to Open.

This is actually already required to be supported by complying to the FHS.