I had to tinker with settings a bit, and don’t recall exactly what I had to do. I remember it being glitchy, and I was able to get rid of it with one of the graphics options. I’m using Chiaki4Deck, which is a fork of Chiaki specifically made for Steam Deck, in case we’re talking about different settings.

One thing that possibly rings a bell is the window behind the game (the Chiaki app where you pick a console) is still open in the background which could cause flashing and glitching. Have you tried running it in Desktop mode?

Also, sometimes it doesn’t connect and the only way to get it to try again is by resetting the PS5. Once it’s connected, it works fine.