Hi,
If you perform an in-place upgrade through the Settings or by using the Windows 11 Installation Assistant, your files and apps should remain unaffected. Everything is expected to stay intact.
However, since every system's health condition is different, it is always a good idea to back up any important files beforehand in case something unexpected happens during the process.
To reduce the risk of issues during the upgrade, I recommend running a few system scans to check for and fix any underlying problems such as system file corruption. Here is how you can do that:
Type cmd in the search bar on the taskbar, select Run as administrator.
Run the following commands one at a time:
sfc /scannow
dism /online /cleanup-image /restorehealth