What I don't like about the immutable approach is that it turns my PC into a dumb terminal locked by the distro Devs and updated at their will.

I think you are misunderstanding how immutable distros work. They can be just as configurable as regular distros and in the case of nixOS it is more configurable than popular distros. The point of immutability is to ensure that the system can't be broken during when it is running by a bad update or install or by user making configuration errors as these are applied during reboot. If the system is broken then a earlier snapshot is booted so you always have a working system. You can setup a regular distro with this atomicity and snapshots but it is not as easy as using immutable distros. Yes tinkering and using native packages is harder in most immutable distros but immutables never were a catch all solution. Use what suits you. I was just a little upset that you claimed that immutables are not in the spirit of FOSS. You can even make your own images(base OS) in distros like fedora silverblue and update your system with those images instead of using what the maintainers provide. It is what uBlue uses