No really related, but I'm surprised that jj has no good GUI.
With so much VC money chasing so many established niches (eg bun -> node), and so much potential growth for jj - especially considering it has so much dev interest, and has the advantage of not requiring lock-in [a jj repo can be converted to a regular git repo].
There's https://github.com/keanemind/jjk for VSCode users. There are also tickets to add jj support in Helix and Zed, so that's promising.
See https://github.com/jj-vcs/jj/wiki/GUI-and-TUI for a standalone GUI and two VS Code plugins. None of the GUIs there are fully-featured, so sometimes you have to imagine what it could become, but each one is usable. The two VS Code plugins can be used at the same time and complement each other somewhat.
jj as effectively used is a git UI. There's an experimental self-hosted backend that nobody uses (and is disabled in release builds), and there's a piper backend in Google, which is enough that people call it a VCS of its own rather than a git UI, but there's nothing stopping some other tool building the same primitives on top of git directly without jj as an intermediate layer. As I understand it, to some extent, that is GitButler.