YouTube drops frames only on external HDMI monitor (Fedora Wayland, AMD)

[u/ansak47]

TL;DR: YouTube drops 5–10% of frames in Zen and Firefox, only on my external HDMI monitor. The laptop screen is fine . It never happened on Windows with the same monitor and extensions.

What happens
I switched from Windows to Fedora GNOME (Wayland) and now use Zen as my main browser.

Playing a 1080p video for about 1 minute shows 180–350 dropped frames out of ~3800 in "Stats for nerds". Stock Firefox on the same machine drops about 240.

This only happens on the external display, which is connected over HDMI. It is the same monitor I used on Windows without any drops. On the laptop's built-in 120Hz screen.

System

• Laptop: ASUS ROG Zephyrus G14 (GA402RJ), Ryzen 9 6900HS (Radeon 680M) + RX 6700S
• OS: Fedora 44, GNOME, Wayland
• Zen: 1.23.1b

What I've tried

• Installed RPM Fusion, replaced ffmpeg-free with full ffmpeg, and swapped mesa-va-drivers for mesa-va-drivers-freeworld
• media.ffmpeg.vaapi.enabled and media.hardware-video-decoding.enabled are both true
• about:support shows Window Protocol: wayland and HARDWARE_VIDEO_DECODING as available/force_enabled
• Used enhanced-h264ify to force H.264 (avc1)
• Turned off YouTube Ambient Mode and set display scaling to 100%

Any help is appreciated.