Hi pseudonymLT
I am Dave, I will help you with this.
The only added security in Windows S Mode is the inability to install 3rd party software, and all Microsoft Store apps are verified by Microsoft as being safe.
Most people that purchase a PC with Windows in S Mode do find they need to switch out of S Mode to install the software they need to use on the PC, and switching out of S Mode is perfectly safe to do, provide you only install software from genuine developers websites, there is then no extra security risk, and whether in S Mode or Windows 11 Home, Defender will continue to protect your PC against malware threats.
Switching out of S Mode to Home is free, it is a one way operation, and it does not cause any performance issues either.