UI-Calculator | Calculator with clean UI | Apps library

I'm writing a simple gui with a QGraphicsScene. Inside this scene i have 2 simple XY axis and I have a function to retrieve the position of my mouse click on the scene.

I added a simple movable ellipse to my scene and I'm retrieving it's position (at the moment it's only an on click detection, later I will implement a signal for its movement)

Here's the code:

View.py:

\EDIT: simplified code to minimum.

I'm not able to connect button.clicked to the function in MVC approach. When debugging the code, all works fine for some time (2-5 clicks) and than no reaction to click. When I run the app in normal mode (no debug) no reaction to click at all. No Errors whatsoever.

I'm trying to follow example from here (MVC model): https://realpython.com/python-pyqt-gui-calculator/#creating-a-calculator-with-python-and-pyqt, which works fine. I tried some other examples from web, and also work fine, so seems problem with my code, and not the installation/configuration issue.

I'm completely clueless now and not even sure what to ask google...

Below the code:

I'm trying to build calculator based on tkinter. I also follow tips from there. Program for sure is still in progress. I'm currently stuck because of this error:

AttributeError: 'Calculator_GUI' object has no attribute 'main'

I have no idea how to get to work communication between both classes. I'm also asking for short review of what already is done. Thanks in advance! Here's the code:

I'm brand new to Python and Tkinter. I've googled to figure out how to change Input Text Box font size but am at a loss. I found out how to increase global font size and it works:

Can tell me the magic spell for increasing font size of text box?

Here is the Python script: