Qt 5.11 is gone

We use Qt 5.11.3 in SuperBuild, but it seems to be gone, both from https://download.qt.io/new_archive/qt/ and https://download.qt.io/archive/qt/. SuperBuild was using Qt 5.14.1 before 1ec8060a (in Sep 2020), which mentions a compatibility problem with CentOS 6.

Since CentOS 6 is EOL, maybe we can revert that commit? Also, where's the list of supported platforms? I think there used to be one, but I can't find it.