I recently noticed that when I connect to VPN from Pop_OS (based on Ubuntu 19.10), the communication continues on the regular adapter via IPv6 in addition to the VPN interface.

This is obviously not ideal, because if we’re using the VPN for privacy, this leaks our IP address and we can be traced back without any effort. The best solution would be to completely disable IPv6 address assignment at the kernel level (by editing GRUB), but I generally use it for other purposes, so I only want to disable it when I’m connected to the VPN.