calibre ebook-viewer gives empty window

[jagdpanther]

ebook-viewer from both calibre-7.26.0 and calibre-8.4.0 gives a blank window when I attempt to display an .epub file. (I do not use the calibre application, only ebook-viewer which comes with calibre. ... I find that ebook-viewer is better at displaying .epub files and okular is much better at .pdf)

Here is an example of the command line output. A few months ago this would work without issue:

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 ]$ ebook-viewer LPM_255-22.epub 
No native pixmap.
Compositor returned null texture
No native pixmap.
Compositor returned null texture
...

Here is a work-around that "fixes" the issue:

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$ QTWEBENGINE_CHROMIUM_FLAGS="--use-gl=disabled" ebook-viewer LPM_255-22.epub 

I found that "fix" at https://bbs.archlinux.org/viewtopic.php?id=305308.

Is there some use flag I should be using somewhere? Here are the use flags for my installed calibre and qtwebengine:

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   dev-qt/qtwebengine
Installed versions:  6.9.1-r1(6/6.9.1)^t(03:57:26 PM 06/28/2025)(alsa jumbo-build opengl pdfium pulseaudio qml system-icu widgets -accessibility -bindist -custom-cflags -designer -geolocation -kerberos -screencast -test -vaapi -vulkan -webdriver)

 app-text/calibre
 Installed versions:  8.4.0^t(09:05:16 AM 07/26/2025)(font-subsetting system-mathjax udisks -ios -speech -test -unrar -verify-sig PYTHON_SINGLE_TARGET="python3_13 -python3_11 -python3_12")