Hi,
I recently started using Redream and have the same issue. Looking around, it seems to be an issue on some AMD cards/APUs, and how the emulator was programmed, causing 'artifacts' (glitchy looking graphics). Latest drivers don't seem to resolve for anyone, but the devs appear to be working with AMD support on it.
It seems like a nice easy to use Emu, but I'll probably use Flycast or Demul for now.
Some links in regards:
https://community.amd.com/t5/drivers-software/artifacts-in-redream-emulator-regression-in-windows-gl-driver/td-p/578904/page/2
Also on Steamdeck:
https://gitlab.freedesktop.org/mesa/mesa/-/issues/2253