Hi, I'm Bernard, a fellow Windows user. I'm happy to help!
To remove all your personal information on your device, and since you want to sell it, I recommend doing a reset and fully cleaning the drive, which will reinstall Windows and remove third-party apps and personal data on the PC. To do that, kindly follow the steps below:
Note: The process will remove everything on the PC, including personal files, apps, and settings. If you are okay with that, kindly follow the steps below.
Go to Settings > System > Recovery > Reset PC > Remove Everything > Local reinstall
Click "Change settings"
You can choose "Delete files from all the drives" to wipe out all the data even on other hard drive, or you can also choose another options from the list.
Follow the prompts to reset.
For reference: https://support.microsoft.com/en-us/windows/reset-your-pc-0ef73740-b927-549b-b7c9-e6f2b48d275e
You can also refer to the link below for further steps:
https://www.digitalcitizen.life/factory-reset-windows-11/
Note: This is a non-Microsoft website. The page appears to be providing accurate, safe information. Watch out for ads on the site that may advertise products frequently classified as a PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the site before you decide to download and install it.
Bernard