With the merge of https://codereview.qt-project.org/c/qt/qtbase/+/479775 in Qt 6.7, auto + QStringBuilder will be fine, so warning about it feels wrong. It might also be interesting to tell users that they could fix the problem by upgrading.
I find it a bit problematic, since we do not know the min Qt version. Like one could have Qt 6.7, but the project requirements are 6.6. IMHO it would be best to document this behavior, but not disable the check completely.
Makes sense, maybe just amend the description saying that the warning could be a false positive, as if the project is targeting Qt 6.7 or above then there's no dangling and thus the warning can be removed.