Returning M1 Mac - Want To Be Sure Data Truly Gone

Hi

I'm going to be returning the M1 Mac Mini that I just purchased and would like to make certain that my data will be unaccessible by either Apple OR whoever ends up with the machine post-return.

I didn't opt to turn on File Vault before I erased it. If I re-install MacOS and then turn FV on and 'Reset All Content and Settings' will that essentially be as if I had done it earlier when I first received the Mini?

Thanks!