Time Machine backups to a Veracrypt volume? I've got an external USB drive with a few VeraCrypt volumes. I want to use one of them for my Time Machine backups. The partition can be deleted entirely, I just wish to keep it encrypted with VeraCrypt. 

Is this possible? When trying to set things up like this, I cannot select this partition as a backup volume in Time Machine settings.

I know I can also create and format a regular partition and use that in Time Machine, and use macOS' or Time Machine's own encryption. But I prefer VeraCrypt.

Note that I'm not using a VeraCrypt container, but an actual partition. Which is then mounted and formatted with regular HPFS+, so I would say after mounting it's virtually the same as without VeraCrypt. But somehow Time Machine won't allow me to select this volume...?
You need to add the partition manually. In Terminal type

sudo tmutil setdestination -a / Volume/YourBackupVolume


Check your Time Machine destinations with tmutil destinationinfo before and after adding the new Volume.