@Vartto 

Make sure you are with the latest FW for your router.

Here's how to update the router FW (case 1).

Forget this wi-fi network on your iPad and login again.

@Vartto 

Please try terziyski's suggestions first to see if any will help resolve the issue.

You can also check my suggestion in the following thread, it seems you're reporting the same:

https://community.tp-link.com/us/home/forum/topic/228716

"We share what we have confirmed about the "Network is blocking encrypted DNS Traffic" error with the community users.

Ever since iOS 14, Apple started supporting encrypted DNS, and sometimes you might get this“ privacy warning: this network is blocking encrypted DNS ” notice on your iOS devices when they are connected to a network that did not support encrypted DNS. The Archer routers don't support encrypted DNS now, but they can forward the traffic to the DNS servers without an issue.

Try figuring this out, you can try the following:

1. Go to the Wi-Fi Settings of your iOS devices, forget/delete the network, then reconnect to it again. Check and confirm if the privacy warning will disappear.

2. If that doesn't help, try changing the DNS servers on the router to 8.8.8.8 and 1.1.1 (Under Advanced > Network > Internet).1 manually, then go to the Wi-Fi Settings of your iOS devices, forget/delete the network, then reconnect to it again."