Assuming you know how to remove the drive; the best choice beyond degaussing the platters is to use a total wipe utility. BCWipe is my choice; bleach bit is also popular.
Remove the drive. Plug it into a SATA (or ATA) to USB adaptor
like this one of which I use for my SSDs.
Plug the drive into the adaptor. Plug the adaptor into the USB port on another computer.
I don’t use bleach bit but for BCWipe you can use multiple settings at once.
Do not format the disk if you haven’t already, it slows the process down.
I use Random, secure erase (if the drive supports it), DOD, 12 binary. (Random sets of 12 1s and 0s, breaking standard 8-bit words). In that order.
Even on SSDs where secure erase is most useful in overriding the controller to wipe provisioning), I found that set in that order to be around 95-99% affective even with expensive programs like Remnants XX 2021.
You can then reformat and partition safely.
Random is just that. Totally random garbage. It actually dates back to the 70s and 80s where an ASCII random test generator would write nonsense to a tape until it ran out of room.
Secure erase is found on quality SSDs and flash drives and some hard drives. It’s controller implemented and allows qualified utilities access to over provisioning storage.
DOD uses a full block three pass. 0, 1, random.
12bit binary uses random 12bit strings based on FAT-12 tables.
BCWipe is available from Jetico. It’s used by the US government and most computer resellers.