Hi Soren, Thank you for looking into this. Unfortunately I have almost no memory of this beyond what is in the bug report.
Four years ago those were the missing dependencies. I am not at this time doing any qt-related development and so I do not know if this is still accurate. I guess you could do what I did back then - install qtwebengine5-examples in a minimal Debian VPS or chroot and then see what is needed to make the examples work. Best Wishes, --Mike