AdGuard DNS blocks connections to Duolingo’s ads endpoints so you will not be shown any 3rd party ads. The asterisk is: it will still show you ads for Super Duolingo but those are shorter, way less annoying, and will never be double-played. I just turn off the speaker for 15 seconds and let the ads play while I do literally anything else.

You can also use this trick to get unlimited free energy. Note that in the current (Android) version, the in-lesson watch ads to gain energy buttons don’t work, so you’ll want to stock up on energy before starting a new lesson.

Here’s how to set it up for both iOS and Android: https://adguard-dns.io/en/public-dns.html

There’s no need to bother with option 1 which tells you to install an app. Option 2 is what you want.