Comment by p1mrx

  $ host www.tailscale.com
  www.tailscale.com has address 76.76.21.21  # Vercel
  www.tailscale.com has IPv6 address 2600:9000:a51d:27c1:6748:d035:a989:fb3c  # Amazon
  www.tailscale.com has IPv6 address 2600:9000:a602:b1e6:5b89:50a1:7cf7:67b8  # Amazon

IPv4 uses a Let's Encrypt certificate, while IPv6 uses an Amazon certificate.