For Juniors it's tough (in general, though it's always been tougher in rubyland), because even the most well organized codebases tend to turn into a bit of dynamic magic spaghetti that can be hard to follow if you're not familiar with Ruby's dynamic nature. Getting newcomers to the language/framework onboarded to old projects (and most Rails projects will be old ones these days) can be a bit of a mess and take a lot of time and effort, so a lot of companies are weary of getting juniors.

That said, if you can display you have knowledge of the more important Rails libraries like ActiveRecord, ActiveJob, how Rails handles the MVC pattern etc., then your chances are much better. It's a bit of a magical framework when you first start working with it, so it's important to know what it does behind the scenes, at least a tiny bit, since otherwise it's easy to get lost.