My PhD work is too simple. I don't feel good about my work, my abilities and my future career
One reason that people like yourself see their own work as &quot;simple&quot; is just that they are the world's foremost expert in that narrow subfield. They (you) know it better than anyone and you've lived with it for a long time so you see how it fits together. This is related to Imposter Syndrome, of course.
Your dissertation and degree aren't the end of your career, but the beginning. You've crossed one &quot;finish line&quot;, the degree, but that opens out into a world of opportunity. You aren't limited now to what you have done in the past but can start to move to adjacent areas if you wish. The degree process is a pretty narrow funnel, but, once through it, the opportunities open again.
Don't be discouraged. Leverage what you have into what you want.