VRR causes monitor to drop into scaler service menu (RX 9070 XT + Samsung Odyssey G5, works fine on Bazzite)

Your system information

• Steam client version: 1785799196
• SteamOS version: 3.8.16 (also reproduced on 3.9)
• Opted into Steam client beta?: Yes
• Opted into SteamOS beta?: Yes
• Have you checked for updates in Settings > System?: Yes

Hardware:

• Desktop PC running SteamOS
• GPU: AMD Radeon RX 9070 XT
• Display: Samsung Odyssey G5 (LS27AG520P), connected via DisplayPort, firmware M-A5200GGZA-1004.4 (latest available per Samsung support)

Please describe your issue in as much detail as possible:

Enabling VRR (Steam Settings → Display → Allow Variable Refresh Rate) in Gaming Mode causes the monitor to lose sync and drop into its internal scaler service/diagnostic menu (Novatek G52A chip info screen) instead of displaying content normally. This happens consistently, on every boot, as soon as VRR is toggled on. Disabling VRR resolves the issue immediately and the display works normally otherwise (including at high refresh rates without VRR).

This is reproducible on both SteamOS 3.8.16 (stable) and 3.9 (preview), so it is not fixed by the latest available SteamOS branches.

Importantly, this same GPU + monitor combination works correctly with VRR enabled under Bazzite (Fedora Atomic-based, using a significantly newer Linux kernel and Mesa than SteamOS's current branch, also running Steam Gaming Mode / gamescope). This strongly suggests the underlying fix already exists upstream in amdgpu/Mesa but has not yet been backported into the kernel branch currently shipped with SteamOS.

Expected: VRR should engage cleanly, matching behavior seen on Bazzite with the same hardware.
Actual: Monitor drops signal and displays its internal Novatek G52A service/debug screen whenever VRR is enabled.

Steps for reproducing this issue:

1. Connect a Samsung Odyssey G5 (LS27AG520P) monitor via DisplayPort to a desktop PC with an AMD Radeon RX 9070 XT running SteamOS in Gaming Mode.
2. Go to Steam Settings → Display and enable "Allow Variable Refresh Rate" (VRR).
3. Observe that the monitor loses signal/sync and shows its internal Novatek G52A scaler service/debug menu instead of the desktop/game output. Disabling VRR immediately restores normal display.

Start by reproducing the issue from Steam Settings → Display with VRR enabled on the listed RX 9070 XT and Samsung Odyssey G5 setup. Compare the SteamOS kernel and Mesa versions with Bazzite's, then verify that the monitor keeps normal sync and displays Gaming Mode content with VRR enabled while disabling VRR still restores it.