It’s been years and years since I set foot in a Game Stop (US equivalent of the store you mentioned) but they would also “buy” any functional game you brought in. However, you would be lucky to get more than for $1 in store credit towards another used game for anything other than a new release.
There’s a firefox extension that upgrades the twitch player and blocks ads. Can’t remember the name but it was easy to find when I searched for it.