If you decide to switch back after 10 days you will need to perform a clean install of Windows 10. You have about 10 days to decide you hate it and revert.
Windows 11 Pro is not available in S mode. If your Windows 10 PC is running the Pro edition in S mode, you need to switch out of S mode to upgrade to Windows 11 Pro. I fit does you can upgrade to Windows 11 in S mode.
Expect it to take longer than a regular Windows Feature update, but you will still be able to use your PC while most of the work is going on. This will depend on factors such as your internet speed and PC.
Where some issues may arise is with older items that require drivers that simply might not get updated as they are no longer supported by their own manufacturers. We don’t see any reason that popular Windows 10 accessories won’t work with Windows 11.