Hi, thank you for your answer. I solved the problem. I performed a router factory reset. After that I run the security test again and it didn't find any vulnerabilities.

Thank you for advice and additional info. I bought a modern router Cudy WR3000 with WiFi-6 support. And it has the last firmware update available.

After checking on tailscale privacy policy, I also suggest to drop tailscale and use mullvadvpn if you live in EU or US (it is great) or protonvpn. You can install WG Tunnel from F-Droid and add wireguard configuration from your VPN provider as well. It is consume only 1-3% during the day on my device.