If I delete an old user can someone recover information from the old user ?

This is what you should do.

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

Emily Booher wrote:

I bought two old mac pros from my uncle and I want to fix them up and sell them.

My uncle sold them to me with important business information/passwords on them.

I would encrypt the drive, then follow the steps to erase the Mac and reinstall the OS as posted by dialabrain.

The encryption process will encrypt all data that is on a location still writable. When you then erase the drive to reinstall the OS, the encryption key will be destroyed and the data inaccessible.

Emily Booher wrote:

It is an old SATA drive and I will only create a new user account then sell it. I will not create very much data, but, I think I might clone the new user account to a ssd then delete the old one.

Just so you know, if you do not follow the excellent advice given, the buyer may wind up with an unusable machine if the OS was downloaded from the app store because the license for it is not transferable and is tied to the Apple ID used to download it. And, if the devices originally came with install media, you need to include them with the sale.

Can you explain what you are trying to do and what your concern is? Are you selling your Mac for instance?

Quite possibly, but less likely over time. Depends on several things such as type of drive and how much data you create that would overwrite the old.

Welcome.

FWIW, you are not supposed to create a user account on a Mac you are selling.