The ERR_QUIC_PROTOCOL_ERROR usually shows up when your browser is trying to use the QUIC protocol—a faster internet connection method mostly used by websites like Google, YouTube, and a few others. If you're using a VPN, proxy, or certain browser extensions, they can sometimes block or interfere with this protocol, which leads to the error. Sometimes it’s just a hiccup with your internet connection or the website itself. So it’s not always something wrong on your end, but it’s worth checking a few things.
A good first step is to go to opera://flags/, search for “QUIC,” and disable the protocol—then restart your browser. If that doesn’t help, try turning off your VPN or proxy if you’re using one, and also test by disabling any suspicious extensions, especially ad blockers. Clearing your browser cache or trying the site from a different browser or network can also help pinpoint the issue. It’s usually a quick fix once you figure out what’s causing the conflict.