HiHo I had the same issue regarding kiwix and pb633.
I ended up compiling a minimal-browser example from this repository:
https://github.com/c3pio-man/pb-qt-3/tree/6.1
It is really a minimal example using qtwebengine (like the default browser I think) but it works fine on my device (except auto rotation) and is enough for my demands.
Hope it helps somehow.