In IPython, how do we do, ie. what key stroke we should perform, to get into a new line inside the current input block without executing or exiting it ?
Hello,
do you mean as in the new line character: '\n'
total = 55.00
print(f'\nHello, this is the current total cost: ${total}.')
Note that a new line character has been added at the very beginning of the line. This will lower the printed line by one line space. You can add multiple in series if you so choose to.
If you are in a function def or something that is not complete it automatically inserts new line without executing, but if you want to enforce it in macos it is ctrl+o 
Control-O
Yes, IMHO is the concluded solution