Hello guys! I want to ask you a few questions about DNS: 1) if my router is from my ISP and it needs PPoE access (username and password) does that mean that I can't change DNS? Are these two thing connected or not? I've no option to change the DNS in my router 2) if a certain device like a pc or phone has set a manual DNS like opendns one but the router has its own DNS, does my ISP still get the logs?
The DNS your computer is using is always specified and controlled by your computer. You can configure any computer to use any DNS you want, and in theory no other DNS should be used other than what you specify. You'll have to disable DHCP configuration on the computer to do this.
Your ISP will always be able to log which sites you visit (although not necessarily what you're doing on them, if the connection is secured with HTTPS/TLS, etc.), unless you're using an encrypted tunnel of some kind such as Tor, I2P or a VPN.