The so-called "S mode" actually refers to "Windows10 S", designed to allow other versions of Windows 10 (such as Home, Professional, and Enterprise) to switch to this feature-restricted SKU.
whenMicrosoftAfter announcing the "S mode" in the Windows 10 April 2018 update (1803), it promises users the freedom to switch to full-featured Windows 10.
Unfortunately, the company has never promised to reverse the operation. After all, rolling back to Windows 10 S means that you need to perform a factory reset to clean up all Win32 software.
For the user, setting this feature in the app does cause a lot of misunderstanding, so many people feel that they can switch between the two modes.
In February of this year, Microsoft unexpectedly gave a step-by-step guide to switching to "S mode" on the Feedback Hub Quest (which should have been used internally only).
At present, it seems that if there is no device recovery image, the "S mode" switching function will not return to Windows 10, or even appear in Redstone 5.