How to erase an older MacBook completely to give away to a friend

This support article describes what to do before selling or giving away your Mac. --> What to do before you sell, give away, trade in, or recycle your Mac - Apple Support

Make sure you do a backup if you have not already transferred content.

You only "lose" things from iCloud if you delete them on a device while signed into iCloud on the device. iCloud works on the basis of what you do one one device is reflected in everything else connected to iCloud as well as whatever is stored on tie iCloud account at that time. Sign out of iCloud on the device and that basically cuts the connection between the device and iCloud. After that you could delete them individually and nothing would happen to them in iCloud, but there isn't any point in doing that if you are doing an entire reset of the device. Just pay attention to all the steps in the article I provided.

If you ever created a firmware password on that Mac, be sure to turn it off before giving the Mac to your friend. This password is not set by default, but if you did set one, you wouldn't want to leave that as a "ticking time bomb" for a friend to discover "the hard way."

Set a firmware password on your Mac - Apple Support

"When you set a firmware password on your Intel-based Mac, users who don't have the password can't start up from macOS Recovery or any disk other than the designated startup disk."

Using Apple's instructions it will behave as if the person had just opened the box sent by Apple. It won't necessarily have the newest OS but the next user can then use Software Update to get anything newer.