Created attachment 181729 [details]
output of edid decode when X34P is set to accuracy and the other to efficiency

SUMMARY
[Bazzite 42]
Mild 1Hz white/black screen flicker occurs on one display (Acer X34P) in a dual-monitor configuration under KDE Wayland on AMD GPU. 
The issue is resolved by setting "Color Accuracy" to "Prefer accuracy" in display settings.

STEPS TO REPRODUCE
Use two monitors:
    X34P at 120Hz (DP-2)
    Secondary at 120Hz or 144Hz (DP-1)
Ensure both are enabled on KDE Wayland
Set "Color Power Preference" to "Prefer efficiency" specifically the X34P
Open a fullscreen window (e.g. game or video) on one display
Move mouse in/out of fullscreen or change focus
Only observed on YT playback:
    also flickers when audio level change indicator pops in/out
    also flickers when YT seek bar pops in/out

OBSERVED RESULT
Full-screen white flash on X34P when mouse moves out of fullscreen window
Full-screen black flash when focus returns
Flicker rate is ~1Hz and consistent
Only occurs on one screen
Does not happen:
    When both monitors are at 60Hz
    If either monitor is at 60Hz while the other is 120Hz
    On an X11 session
    (did not try gnome, I did not want to install it :P )
also happens when refresh rate is maxed for both X34P (120Hz) and the Acer 

EXPECTED RESULT
No flickering. Smooth refresh switching across displays.

SOFTWARE/OS VERSIONS
from kinfo:
Operating System: Bazzite 42
KDE Plasma Version: 6.3.5
KDE Frameworks Version: 6.14.0
Qt Version: 6.9.0
Kernel Version: 6.14.6-105.bazzite.fc42.x86_64 (64-bit)
Graphics Platform: Wayland
Processors: 16 × AMD Ryzen 7 5800X3D 8-Core Processor
Memory: 31.3 GiB of RAM
Graphics Processor: AMD Radeon RX 7900 XTX
---
Monitors: Acer X34P, Acer XV272U

ADDITIONAL INFORMATION
Disclaimer: I mostly talked with ChatGPT about this because I could not find anything on the webs, so the report is mostly made by me asking it to generate one, since it knew all the info and it was faster. I checked the accuracy. The kinfo report, edid-decode, and kscreen-doctor are of course directly from terminal, I am not this dense.

If I missed anything, sorry. Please ask nicely, I am new. I tried a bunch of stuff to fix this. In the last lines of the edid-decode you can see the slightly different refresh rates. (Detailed Timing Descriptors section). 120Hz is relevant one here.

output of kscreen-doctor -o when X34P is set to accuracy and the other to efficiency:
Output: 1 DP-1
	enabled
	connected
	priority 2
	DisplayPort
	Modes:  1:2560x1440@144!  2:2560x1440@120*  3:2560x1440@60  4:2560x1440@60  5:1920x1200@144  6:1920x1080@120  7:1920x1080@120  8:1920x1080@60  9:1920x1080@60  10:1920x1080@60  11:1920x1080@50  12:1600x1200@144  13:1680x1050@60  14:1280x1024@75  15:1280x1024@60  16:1440x900@60  17:1280x960@60  18:1280x800@60  19:1152x864@75  20:1280x720@60  21:1280x720@60  22:1280x720@60  23:1280x720@50  24:1280x720@50  25:1024x768@75  26:1024x768@70  27:1024x768@60  28:832x624@75  29:800x600@75  30:800x600@72  31:800x600@60  32:800x600@56  33:720x576@50  34:720x576@50  35:720x480@60  36:720x480@60  37:720x480@60  38:720x480@60  39:640x480@75  40:640x480@73  41:640x480@67  42:640x480@60  43:640x480@60  44:720x400@70  45:1600x1200@60  46:1280x1024@60  47:1024x768@60  48:1920x1200@60  49:2560x1440@60  50:1920x1080@60  51:1600x900@60  52:1368x768@60  53:1280x720@60
	Geometry: 0,0 2560x1440
	Scale: 1
	Rotation: 1
	Overscan: 0
	Vrr: Never
	RgbRange: Automatic
	HDR: disabled
	Wide Color Gamut: disabled
	ICC profile: none
	Color profile source: sRGB
	Color power preference: prefer efficiency and performance
	Brightness control: supported, set to 100% and dimming to 100%
Output: 2 DP-2
	enabled
	connected
	priority 1
	DisplayPort
	Modes:  54:3440x1440@60!  55:3440x1440@120*  56:3440x1440@100  57:3440x1440@85  58:3440x1440@50  59:1920x1200@60  60:1920x1080@60  61:1600x1200@60  62:1680x1050@60  63:1280x1024@60  64:1440x900@60  65:1280x800@60  66:1280x720@60  67:1024x768@60  68:800x600@60  69:640x480@60  70:640x480@60  71:1600x1200@60  72:1280x1024@60  73:1024x768@60  74:1920x1200@60  75:1280x800@60  76:2560x1440@60  77:1920x1080@60  78:1600x900@60  79:1368x768@60  80:1280x720@60
	Geometry: 2560,0 3440x1440
	Scale: 1
	Rotation: 1
	Overscan: 0
	Vrr: incapable
	RgbRange: Automatic
	HDR: incapable
	Wide Color Gamut: incapable
	ICC profile: none
	Color profile source: EDID
	Color power preference: prefer accuracy
	Brightness control: supported, set to 100% and dimming to 100%