There are few more hardcore options , but difficulty level really depend on phone/os you are using. Some might require rooted phones, which is always considered as less secure than not having root (unless you really know what you’re doing with your root!).
There are some apps that allow you to clone/duplicate same application and have it running concurrently. Different methods have various limitations, and honestly, I don’t even know how link from an email will know what app should be logged in. I haven’t seen or read about any attempts to duplicate Monzo app, maybe someone had done it and is willing to share?
You would need to google for methods that match your device and try them out. That being said, it’s a very long shot, and I’m not sure I’d be bothered myself to try it out.