From the Emacs manual:
Auto-saving does not normally save in the files that you visited,
because it can be very undesirable to save a change that you did not
want to make permanent. Instead, auto-saving is done in a different
file called the "auto-save file", and the visited file is changed only
when you request saving explicitly (such as with ‘C-x C-s’).
In other words, auto-saving saves a copy of your work (your buffer), under a different file name. It does not save the buffer you are editing to the disk file it is visiting.
Read the sections of the manual about this to understand more, starting with node Auto Save.
You can find this information yourself, by asking Emacs:
C-h r opens the Emacs manual. Then
i searches the index, using completion, for index entries you type.
In this case,
i auto save RET takes you directly to node Auto Save. But
i auto TAB shows you all of the index entries that start with
auto. Besides the entry
Auto Save Mode (and some entries that have nothing to do with auto-saving) you see several entries that start with
auto-save for remote files
Choose any of them to visit the relevant manual node.
Experiment a bit to get familiar with using
i. You can also search the entire manual using
C-s (incremental search).