While trying to compile it, I ran into a few issues. Firstly, (strawberry) perl wasn't working, so I used MinGW (mingw1120_64) included in the Tools folder that the maintenance tool made and that worked. I got a warning that without perl some stuff doesn't have to work properly. Secondly, I got an error that QtWebEngine won't be built, but I don't remember what was the error (QtPdf also didn't build, because I don't have nodejs 12.0 installed, but I don't care about that). The build process also stopped once, because I ran out of storage space.

Anyway, here are the errors that I'm currently facing:

error: C:\Qt\6.5.2-static\plugins\networkinformation\libqnetworklistmanager.a(qnetworklistmanagerevents.cpp.obj):qnetworklistmanagerevents.cpp:(.text$_ZN25QNetworkListManagerEvents24checkBehindCaptivePortalEv+0x6a): undefined reference to `__imp_VariantInit'

error: C:\Qt\6.5.2-static\plugins\networkinformation\libqnetworklistmanager.a(qnetworklistmanagerevents.cpp.obj):qnetworklistmanagerevents.cpp:(.text$_ZN25QNetworkListManagerEvents24checkBehindCaptivePortalEv+0x13d): undefined reference to `__imp_VariantClear'

error: C:\Qt\6.5.2-static\plugins\networkinformation\libqnetworklistmanager.a(qnetworklistmanagerevents.cpp.obj):qnetworklistmanagerevents.cpp:(.text$_ZN25QNetworkListManagerEvents24checkBehindCaptivePortalEv+0x1ea): undefined reference to `__imp_VariantClear'

error: C:\Qt\6.5.2-static\plugins\networkinformation\libqnetworklistmanager.a(qnetworklistmanagerevents.cpp.obj):qnetworklistmanagerevents.cpp:(.text$_ZN25QNetworkListManagerEvents24checkBehindCaptivePortalEv+0x261): undefined reference to `__imp_VariantClear'

Edit:
I forgot to mention, this is the modules included in my .pro file: core gui websockets network

And the included files in my header file (not everything):

#include <QtWebSockets/QWebSocket>
#include <QJsonObject>
#include <QJsonDocument>
#include <QDebug>
#include <QHostInfo>
#include <QNetworkInterface>