What can Jungian typology teach us about the invisible struggle of the INFP personality type? What is the nature of the shadow and how does it influence the INFP? 

The INFP Consciousness
Inside the INFP is a deeply philosophical and introspective question: What are people underneath their masks? What are people’s hidden intentions? Why do people do the things they do? If you have felt this tug of this question, INFP, know this: your entire worldview and everything you see and ever learn depends on how you answer it.
As an introvert, your natural orientation starts with what is within, and everything outside is shaped by your inner compass. As a perceiver, you have a multitude of purposes and options available before you, and you can always change and adjust. The introverted perceiving type is predominantly an advisor: this is the starting point of the INFP and the INFPs base comfort zone and frame of mind. So in times when you feel a loss of stability and control, this is where you can reclaim it: in yourself. 
What is the shadow?
The shadow is both positive and negative. It represents things that we do not like that we do not realise that we dislike, and it represents things we like that we do not realise we like. So what does an INFP like that they do not dare to dream of? What does an INFP enjoy that they don’t dare to consider? Are there perhaps ideas, visions, insight, lurking beyond that the INFP does not wish to confront? Are there important events happening around the INFP that the INFP needs to learn to speak up about?
In the shadow lies the secret of love and also hidden traumas. The shadow is in it’s nature a giant blindspot. We face it every day but we do not recognise it’s power. Often, we will blatantly deny it’s power or influence over us.
We will dismiss it as something stupid, unnecessary, or impossible. At other times, we will regard it as something magical, unexplainable, as we recognise it’s value, but do not understand it’s process.
The INFP Shadow
To understand your shadow you have to come to gain an understanding of the ENFJ personality type and how it resides and influences you. Yes, the ENFJ reflects your inner muse: it’s from the shadow that you gain energy and passion in times when you feel a loss of stimulation and purpose. The ENFJ is driven by harmony: and the question is, how does this functions interact with your base needs?
As an idealist, you will naturally value the intuitive values such as freedom, privacy, and discovery. You’ll also recognise the significance of feeling, people, values, virtue, and compassion. But you don’t always recognise the significance and the importance of these things. And you don’t always understand why some things are important and why some things have to be done a certain way. Why do we need diplomacy? And why do we need to share our feelings and our beliefs with other people? Are not beliefs something that should be kept personal? Isn’t it more important to call things out for what they are, than to wrap up the message in a way that indicates that you’re nice and understanding? 

The ENFJ

The ENFJ promotes good initiatives, celebrates what is right, and argues against what is wrong. The ENFJ is diplomatic and finds ways to align human interests and values when possible. The ENFJ speculates about what can be and plots how things can be improved. And the ENFJ deducts what will happen next and how things are changing.

The INFP

The INFP reasons about why things are good and what makes something right, and asks questions about why things are wrong. The INFP reports about the state of people, how they feel, what they are going through, and why people do what they do. The INFP becomes a catalyst who changes up the world and identifies options. And the INFP philosophises about the meaning of life and the nature of the world.
There is no inherent conflict between these different strategies, as both fulfill the core aim of the idealist: positive change and deeper connection and understanding. The NFs all share the same dominant priorities but they are prone to dismissing each others strategies. We can be suspicious of the shadow, thinking the ENFJ is just a secret ESTJ putting up a show. But we can also overidealise it. Sometimes we judge what we do not understand. This usually stems from fear and shame within ourselves. We might hold envy or jealousy to others. Especially if they’re good at something that we struggle with. Or if we’ve made mistakes in the past or harbour traumas that distort our perspectives of others.
When an ENFJ is able to achieve something the INFP appreciates, they may dismiss the ENFJ’s approach as magical, crazy, or “a lucky coincidence.” Of course, it is neither, it is deliberate, and the ENFJ knows exactly what they’re doing.
But to the INFP, the process may look disorienting, confusing, or mysterious. This is also why we tend to look at our shadow type as a kind of muse. A crazy, fickle, absurd source of energy, passion, and inspiration. Someone or something we can’t control that holds mysterious power or potentially dangerous consequences. 
What I have learnt is that an INFP needs to trust their own power and their own methods but to recognise the strengths and opportunities offered by the ENFJs around them. I also encourage INFPs to let themselves be naturally inspired by the ENFJs affection, emotionality, and passionate speech. Speak the way you do, but take it one step further, do things you are comfortable with, start out where you are, but then take things one step further. Do ten things you would do, and then one thing an ENFJ would do.
Follow your natural line of reasoning, and then open yourself to the crazy an ENFJ could offer. Therein lies a great opportunity to grow. The muse often represents our level of difficulty at which we play life. Just doing things we usually do, we can get stuck in a rut, we can end up with just more of the same, but if we do what we usually do, and then something different, there’s always change, always opportunity, always potential. And always chances to grow.