What to encrypt : Time Machine or an external SSD via APFS ?

Hello everyone!

When you want to encrypt an external SSD for Time Machine, what do you advise?

Format it in APFS (encrypted)

or / and

Choose to encrypt the Time Machine backup ?

To be more detailed :

I got a new external SSD, I can format it as an APFS (encrypted) drive.

So I have to choose a password to access at whatever is inside.

In another hand, when we choose to use an external drive for Time Machine, it ask if we want to encrypt the backups (no allusion to the format of the drive here).

So, it seems that there is 2 strategy to encrypt an external SSD for Time Machine.

I just would like to know what's the best choice.

Thank you !