Hey, all the tools that you have mentioned are used for UI development.
Tkinter is the python interface to the Tk GUI toolkit that is shipped with Python.
Flask is a web application framework written in Python. You can develop a web application with the help of it.
Django is a widely used framework with Python for web-app development.
All these are the options you can use to create web-application. In freelancing, if you are creating a web-application then you can use the above-mentioned tools. This way these tools are going to help you in freelancing.