Audio only, no video with new player backend (Flatpak, Intel HD 620, Zorin OS 18.1)

Environment

OS: Zorin OS 18.1 (based on Ubuntu 24.04)

Architecture: amd64

GPU: Intel HD Graphics 620 (Kaby Lake)

Shotcut: 26.6.25 (Flatpak from Flathub: org.shotcut.Shotcut)

OpenGL: Mesa Intel(R) HD Graphics 620, Mesa 25.2.8

Vulkan: working (vulkaninfo sees Intel HD 620)

VAAPI: working (vainfo):

VA-API version: 1.20 (libva 2.12.0)
Driver: Intel iHD driver for Intel(R) Gen Graphics - 24.1.0
Profiles include MPEG2, H.264 (Main/High/Constrained Baseline), HEVC Main/Main10, VP8, VP9, etc.
Summary

With the default/new Shotcut video player backend, opening an MP4 file plays audio only with no video visible in the preview.
If I enable Settings → Player → “Use old video player”, the same file plays with both audio and video correctly.

Steps to reproduce

Install Shotcut via Flatpak from Flathub: org.shotcut.Shotcut (version 26.6.25).
Ensure Settings → Player → “Use old video player” is OFF (i.e., using the new player backend).
Open an MP4 video (plays fine in VLC on the same system).
Press Play.
Expected result

Video preview shows the video while audio plays.
Actual result

Audio plays.
Video preview area stays black (no video frames rendered).
Additional information

The issue started after updating to Zorin OS 18.1; the same Shotcut Flatpak worked about a week earlier.

Host graphics stack looks healthy:

glxinfo -B shows direct rendering: Yes, Intel HD 620, OpenGL 4.6, Mesa 25.2.8.
vulkaninfo initializes successfully and lists Intel HD 620 as GPU 0.
VAAPI was initially failing with vaInitialize failed, but is now fixed by:

Installing intel-media-va-driver-non-free (i386 + amd64).
Creating a symlink:
sudo ln -s /usr/lib/x86_64-linux-gnu/dri /usr/lib/dri
vainfo now works and lists multiple decode/encode profiles.
Running Shotcut via Flatpak:

bash

flatpak run org.shotcut.Shotcut
shows only minor warnings (e.g., libDeckLinkAPI.so: cannot open shared object file: No such file or directory and some mp3float overread messages), but nothing obvious about the video pipeline.

Workaround

Enabling Settings → Player → “Use old video player” restores normal behavior (audio + video) with the same files and on the same system.
Request

Please investigate why the new player backend in the Flatpak fails to render video on Intel HD 620 / Zorin OS 18.1, despite a working OpenGL/Vulkan/VAAPI stack on the host.
If you need more logs, I can provide additional debug output or try specific environment variables or builds.

Start by reproducing the black preview with the Flatpak command and an MP4 while Settings → Player → “Use old video player” is off, then compare it with the working old backend. Use the reported Intel HD 620, OpenGL, Vulkan, and VAAPI environment to narrow the new backend failure. Done means the new player renders video frames while audio plays on this setup without requiring the workaround.