Piracy

I'm using qBittorrent's web ui, and you get to the setting from Options (cog symbol)->Advanced tab->Network Interface. Figuring out which network interface is the VPN interface depends on your OS.

My VPN app took a shit in the middle of a download and I think it exposed my IP to some “anti-piracy” bullshit firm that contacted my ISP.

I think you answered your own question.

The same way you can see the ip of your peers on any particular torrent.

This site is kinda cool

https://iknowwhatyoudownload.com/

Many places have laws in place currently stating that you can't be personally identified by your IP. So if you get emails about piracy and copyright issues coming from a law firm representing rightsholders, the best course of action is usually to ignore them. Responding to them is essentially admitting that you're the person they're looking for and that you committed the offense in question.

I suggest you to deactivate IPv6 also and force the killswitch.

Oof, sorry. This will depend on OS and the software you use for FW configs. I am too dumb.

For example, I use UFW on Linux. So for me it's

# Deny all incoming and outgoing traffic by default
ufw default deny outgoing
ufw default deny incoming

# Allow connection to VPN server
ufw allow out to <VPN server IP address> [port] <VPN server port number> [proto] <tcp|udp>

# Allow connection via VPN interface
ufw allow out on <interface name> from any to any

# Enable UFW
ufw enable

That's just one simple way.