Reset Mac to (Out of the Box)

Erase all Content erases all of your content, leaving the OS installed.

Erase all content and settings on Mac - Apple Support

Reinstall macOS reinstalls the OS, leaving all of your content on the Mac.

How to reinstall macOS - Apple Support

macOS is split into a System volume and a Data volume. The two can be independently erased.

Fady-Nahlawy wrote:

What is the difference between Erase All Content & Reinstall macOS?

https://discussions.apple.com/content/attachment/d89d5c10-e78d-4f76-bc08-6af3bd10574b

https://discussions.apple.com/content/attachment/81c246ed-d5f2-4b99-a873-1bc6acc8cbb5

One erases the content

the other one re installs the macOS...

ref:

https://support.apple.com/guide/mac-help/erase-your-mac-mchl7676b710/mac