There are many varieties of bosses. There are those who struggle more or less just with being human beings. Some come with more baggage than they or any relationship could sustainably carry. Some have grown into wonderful leaders skilled in helping others grow in positive ways and with positive impacts.
When we have a struggling boss, we can be a source of positive feedback to them. We can help them make and keep small promises. We can help them become less unconscious of when they impact their world in positive ways. We can build trust by making and keeping small promises. We can model what we want to see. None of these are magical. They simply create the conditions that can support their growth. If they don't have sufficient growth capacity we might need to move on to a boss who does.