@Red1030 

Hi,

Note that big DNS providers (like 1.1.1.1 and 8.8.8.8) will route your requests to servers with other IP addresses.

I suggest you do a Whois lookup for the IP addresses shown by the leak test to see to whom they belong to. In case they belong to the same DNS provider whose DNS server addresses you entered into your router, then I would say everything is good. 

  @woozle 

Hi, 

My internet service provider uses Google. 

I changed and tested various DNS service provider's DNS addresses, for example, quad9, cloudflare and adguard. 

The result is the same. 

  @Red1030 

Ok.

What about your web browser's settings? 

By now, all the major web browsers have a "secure DNS" feature built in. However, if this feature is activated in the web browser, then it will override the DNS settings of the router and there is noting the router could do about it. Therefore, verify that any such feature is switched off in the web browser.

  @woozle 

Secure DNS is disabled. I have also attached computer's ethernet settings. It is now set to default automatic. 

  @Red1030 

Is the "IPv4 DNS servers" address shown on your last screenshot identical to the LAN IP address of your TL-WR845N ?
 

  @woozle 

Yes, that's correct. 

  @Red1030 

Then I don't know why it doesn't work. 

If, for example, the field "DNS Server" for the PPPoE connection has the value 1.1.1.1 and the client devices receive the LAN IP address of the router as their DNS Server's IP address, then the DNS requests of the client devices should be routed to Cloudflare's servers, but not Google's.

As a last resort you could try to update your TL-WR845N to a newer firmware version, but I actually doubt that the current firmware in your router has a bug that defaults the DNS Server to Google's.