Erasing but keeping certain apps

You cannot include any software that you have purchased or downloaded using your Apple ID. Follow these instructions:

What to do before you sell, give away, or trade in your Mac

Factory reset of your Mac - Apple Support

Internet/Network Recovery of El Capitan or Later on a Clean Disk

You will need a fast, working Internet connection, preferably, Ethernet. If you must use Wi-Fi, you will be asked to select your network and enter the network password. This procedure will install the original version of macOS that came pre-installed from the factory.

1. Restart the computer. Immediately, at or before the chime, hold down the (Command-Option-Shift-R) keys until a globe appears.
2. The Utility Menu will appear in from 5-20 minutes. Be patient.
3. Select Disk Utility and click on the Continue button.
4. When Disk Utility loads select the target drive (out-dented entry w/type and size) from the side list.
5. Click on the Erase button in Disk Utility's toolbar. A panel will drop down.
6. Set the partition scheme to GUID.
7. Set the Format type to APFS (SSDs, only if installing Mojave or Catalina ) or Mac OS Extended, (Journaled.)
8. Provide a volume name, usually "Macintosh HD."
9. Click on the Apply button, then click on the Done button when it activates.
10. Quit Disk Utility and return to the Utility Menu.
11. Select Install OS X and click on the Continue button.

Your third-party software such as Office for the Mac and Adobe CC will require that you provide the original installation media as well as the serial codes for each product. You cannot keep copies for yourself.

It's a violation of their terms of use. You may convey them (non-Apple apps) and the serials, but cannot keep your own copies. 32-bit apps can be upgraded to 64-bit apps at some expense.

As far as Apple apps are concerned, they cannot be included on the computer. Once the new owner enables their own Apple ID on the computer, they will no longer be able to update/upgrade the software because the installed versions are tied to your Apple ID.

This is all related to licensing restrictions.