Apple's SSDs are all encrypted at the controller nowadays. No need to rewrite, just reformat and it cycles the key, leaving any recoverable data irrevocably encrypted (until we break modern encryption).
I thought all SSDs did that for wear-leveling purposes.
They do, but consumer ones usually don't implement the additional API (TCG Opal) that lets you lock/unlock the hardware encryption key. Without that capability you can't use it to implement full-disk encryption. They do usually implement the NVMe secure erase feature though, which will rotate it.