Which partition to delete for clean install?

Hi all

I want to sell my old iMac and delete macOS for a clean install. The iMac has a 1 TB HDD which I erased (with security options).

Now here is the SSD I want to erase, but Disk Utility shows two partitions (?). Both SSD are about 250 GB, titled …

1. Apple SSD TS256C MEDIA – SATA Internal Physical • GUID Partition Map
2. Macintosh HD – Core Storage Logical Volumen

Which do I need to delete? Or both?

I had FileVault enabled, so I guess it is enough to just delete it once.

Thanks for helping!