The best I can come up is to grep inside flatpak platform. As in flatpak run --command=sh org.kde.mobile.angelfish then in the opened shell, try to grep files in /usr As for patch, I don't know who to ask. I am mainly in contact with some KDE developers. That type of question should probably belong to freedesktop-sdk IRC/Matrix channel or their issue tracker in gitlab. But try to see first which file has the error message and proceed from there.