Google changed the Safenet check API. It now requires an API key, which current Magisk releases don't have. Thus the "invalid response" message.
If you use an App from the google play store to check your Safetynet status instead (which already HAS...
$IPTABLES -I afwall-wifi-tether -p udp -m owner --uid-owner 1052 -m udp --sport 67 --dport 68 -j RETURN
$IPTABLES -I afwall-wifi-tether -p udp -m owner --uid-ow...
First deactivate the xXx module before the update.
When flashing a full OTA (either through phone updater or through TWRP, doesn't matter) it is irrelevant whether xXx is still active or not - after the flash everything (TWRP, Magisk) is gone an...
Works perfectly for me. My OP6 gets its IPv6 flawlessly from my router (AVM Fritzbox 7580). That requires you receive a valid IPv6 subnet from your ISP, and your router is required to support prefix delegation.
The search function would have been your friend, since this is an issue which is already known longterm (more than a month!).
You messed things up by flashing Magisk 16.7 directly, which broke "DM verity" - hence the error message.