Currently you can only try it by building it yourself, instruction here. https://codeberg.org/solver-orgz/treedome/src/branch/master/docs/building.md
But .deb and nixpkgs update is planned to follow suit though! You can also try an outdated one in https://aur.archlinux.org/packages/treedome-bin.
Tell me what you think about it!
Is it stored in a single folder like joplin does? Can I move the folder around and easily open it after I did that?
Yes and yes. The folder is just a bunch of markdown documents, as well as a hidden folder containing configuration, plugins, etc (json, js, css, etc). The vault is entirely self-contained.