I've tried out jj a little bit personally, but without exaggeration I am using git submodules in every single "real" project I'm actually working on, so lacking support for submodules is a complete non-starter for me :/
What I do is I git clone --recursive and then init a colocated repository. JJ will find the submodules and ignore anything in them, it works decently well.
nasso_dev|10 months ago