Do exactly what Ferdinand told you. No indents if you remove # (it must be flush left). Then when starting the script at your miniconda3 (pytroll) prompt do what I have told you days back. Use the command:
python Sentinel-3A.py 20201217 > DEBUG.txt 2>&1
The screen will stay black for a while. When the prompt returns you will find a text file DEBUG.txt in your script directory. Move this to the desktop with Windows Explorer. Open it with notepad and study it.
If you still cannot find the problem, attach a copy to your next post. (BTW what you have done is redirection of stdout and stderr to a file. It's much easier than trying to send a screen copy of the output.)