Hi. I'm Brian and I will do my best to help you.
It is a one-way street. Once you remove S mode, you'd need to reinstall Windows completely to get it back.
S mode was geared toward people who don't need to use software not in the Microsoft store. Turning off S mode doesn't have a downside if you need to use that software. Apps like Defender will continue to run just fine. So will any program you was installed from the Microsoft store while in S mode.