I do believe Joplin in particular will not be a good companion tool, as it lacks the ability to work with external files directly. Stuff has to be imported fully into it, and then exported to get it back to files. I suppose you could do that, but I don’t know how well it would work—the main thing that might get messy is how Scrivener uses file system modification dates to calculate what needs to be synced back into the project they came from, and an import/export cycle could mess with those.
There are number of tools that do work well with a folder full of text files though. Obsidian is one that in particular has been discussed around here, and it works very well with Scrivener across multiple platforms, or even on the same machine.