reset macbook pro without reinstalling OS

You can't do that.

The OS and any software downloaded from the Mac App Store is tied to your Apple ID, and and as such will require your password to update when it needs to.

You need to completely wipe the Mac so the new user can set it up themselves with their own Apple ID.

You should restore the machine, so that the OS is installed without being tied to any Apple ID, and it can be correctly set up by the new owner with theirs.

Follow the steps in the support document provided by Bob, to correctly wipe the machine so the new owner can set it up. It should take no more than 1 hour to have it wiped and ready to be set up by the new owner.

Follow the directions or sell it as is. The buyer will not be able to use it and your data will be at risk. Just follow the instructions. There are no shortcuts. If there was a shortcut I would have told you rather than telling you what needs to be done. It likely took you three months because you were installing incompatible of useless apps. Resetting according to the instructions I provided should not take you more than an hour at most.

What to do before you sell or give away your Mac - Apple Support