Indeed, you can pretty-print your Google Sheets formulas with Ctrl + Return and Space. But there is a software bug in the current (2019-04) Google Sheets implementation that causes your whitespace changes to not be saved. A workaround is provided below.
The bug is triggered like this:
Google Sheets keeps an internal history about what formulas have been stored in a cell so far.
When you change a formula, it is compared against this history, and whitespace differences are ignored.
When it is found in the cell history, the old version of the formula (including its own whitespace formatting!) is used. When it is not found in the cell history, the formula you just entered is used.
In effect, whitespace-only changes are discarded when editing a formula.
For your whitespace changes to always be saved, your formula has to be always unique in its history (with whitespace differences ignored). You can achieve this by appending a do-nothing-operation to the formula and changing that with every change of your formula. Below are examples. You would choose a new line from the following list on each edit and use it at the end of your formula:
For number formulas:
+ 0 * 1
+ 0 * 2
+ 0 * 3
For text formulas: append the empty string a number of times