Sold MacBook Showing on “Find My” App

As the title says I can see the sold MacBook from months ago on the Find My app. I only realised this because I switched back to an iPhone recently.

I believe I followed the correct process from the Apple website on what to do before selling the MacBook. I signed out of iCloud, reformatted (a couple of times actually), reset NVRAM, etc. I have also changed my Apple ID password and logged out of all devices.

I may have forgot to turn off Find My Mac, but this is a maybe. Either way the new owner clearly never signed into their own iCloud account on the MacBook.

Each time I remove the device it comes back a little while later on my list. Probably because the MacBook goes online again.

What can I do here? Can the new owner have access to my iCloud (I doubt they can)?

Thanks.