I forgot my iCloud Security Code

I bought a new Mac and I used my old apple id. I say old because I haven't had a mac or iphone for several years now. I used to have an iPod Touch and a Macbook at least 6 years ago.

Everything is working fine, I have my apple id accout with two factor authentication and everything.

However, I keep getting this anoying message: "Some iCloud Data Isn't Syncing"

And when I click on "Resume Data Sync" it asks for an iCloud Security Code that I don't remember, if I click on "Forgot Code?" it says: "If you can’t remember the iCloud Security code, you can approve this Mac using another device."

But I don't have any other device. I lost my old iPod and Macbook.

What can I do?

Sorry if it is a repeated question but I haven't found an answer for my specific use case.

Thanks in advance.