Starting with Qt 6.3, on Intel graphics only, visiting https://mozilla.github.io/pdf.js/web/viewer.html in simplebrowser results in a blank PDF being displayed, as the text is rendered white instead of black. Selecting the text confirms its there, just not rendered:

The same happens on Google Sheets:

With the following scenarios, the bug does not show up:

• On Qt 6.2 or 5.15 (note that needs the legacy build of PDF.js to run properly: https://mozilla.github.io/pdf.js/legacy/web/viewer.html)
• With an older mesa version, it seems - I've tried with a Fedora Workstation Live 37 1.7 booted from USB and that looked fine, but booting Manjaro (x86_64, Plasma, Full) shows the bug.
• Setting either of QTWEBENGINE_CHROMIUM_FLAGS=--disable-gpu, QT_XCB_FORCE_SOFTWARE_OPENGL=1 or QT_QUICK_BACKEND=software
• According to one reporter, when using optirun to run on the NVidia GPU instead
• On AMD graphics

Downstream bug: https://github.com/qutebrowser/qutebrowser/issues/7489