The only way to stay on Qt 5.x (as Qt 6.x is not yet ready for production use since the ABI is not stable and many modules like QtWebEngine are missing) would b

The only way to stay on Qt 5.x (as Qt 6.x is not yet ready for production use since the ABI is not stable and many modules like QtWebEngine are missing) would be to fork it, since they will no longer accept patches from the community. Either that, or get every Qt distributer (e.g. Debian, OpenSUSE, Manjaro, etc) to accept your patch.