I have issues with my custom build Qt6 when trying to start Plasmashell.

Cannot mix incompatible Qt library (6.4.2) with this library (6.6.0)

Thread 1 "plasmashell" received signal SIGABRT, Aborted.
__pthread_kill_implementation (no_tid=0, signo=6, threadid=140737224181248) at ./nptl/pthread_kill.c:44
44      ./nptl/pthread_kill.c: No such file or directory.
(gdb) where
#0  __pthread_kill_implementation (no_tid=0, signo=6, threadid=140737224181248) at ./nptl/pthread_kill.c:44
#1  __pthread_kill_internal (signo=6, threadid=140737224181248) at ./nptl/pthread_kill.c:78
#2  __GI___pthread_kill (threadid=140737224181248, signo=signo@entry=6) at ./nptl/pthread_kill.c:89
#3  0x00007ffff3842476 in __GI_raise (sig=sig@entry=6) at ../sysdeps/posix/raise.c:26
#4  0x00007ffff38287f3 in __GI_abort () at ./stdlib/abort.c:79
#5  0x00007ffff40d9d16 in  () at /home/user/kde/qt6usr/lib/libQt6Core.so.6
#6  0x00007ffff40dca06 in  () at /home/user/kde/qt6usr/lib/libQt6Core.so.6
#7  0x00007ffff40c8466 in QMessageLogger::fatal(char const*, ...) const () at /home/user/kde/qt6usr/lib/libQt6Core.so.6
#8  0x00007ffff418182a in QObjectPrivate::QObjectPrivate(int) () at /home/user/kde/qt6usr/lib/libQt6Core.so.6
#9  0x00007fffab0157bc in QSqlDriver::QSqlDriver(QObject*) () at /lib/x86_64-linux-gnu/libQt6Sql.so.6
#10 0x00007fffab00cc40 in  () at /lib/x86_64-linux-gnu/libQt6Sql.so.6
#11 0x00007fffab00da8d in QSqlDatabase::QSqlDatabase() () at /lib/x86_64-linux-gnu/libQt6Sql.so.6
#12 0x00007fff9033cdb6 in Common::QSqlDatabaseWrapper::QSqlDatabaseWrapper(Common::(anonymous namespace)::DatabaseInfo const&) (this=0x5555560e8820, info=...) at /home/user/kde/src/kactivities-stats/src/common/database/Database.cpp:56
#13 0x00007fff9033bebe in std::make_unique<Common::QSqlDatabaseWrapper, Common::(anonymous namespace)::DatabaseInfo&>(Common::(anonymous namespace)::DatabaseInfo&) (__args=...)
    at /usr/lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12/bits/unique_ptr.h:1065
#14 0x00007fff9033b486 in Common::Database::instance(Common::Database::Source, Common::Database::OpenMode) (source=Common::Database::ResourcesDatabase, openMode=Common::Database::ReadOnly)
    at /home/user/kde/src/kactivities-stats/src/common/database/Database.cpp:163
#15 0x00007fff9031ea80 in KActivities::Stats::ResultModelPrivate::ResultModelPrivate(KActivities::Stats::Query, QString const&, KActivities::Stats::ResultModel*)Python Exception <class 'gdb.error'>: Invalid reinterpret_cast
 (this=0x5555560e6340, query=..., clientId=, parent=0x555556110650)
    at /home/user/kde/src/kactivities-stats/src/resultmodel.cpp:55
#16 0x00007fff9031cf40 in KActivities::Stats::ResultModel::ResultModel(KActivities::Stats::Query, QObject*) (this=0x555556110650, query=..., parent=0x0) at /home/user/kde/src/kactivities-stats/src/resultmodel.cpp:987
#17 0x00007fff8a7152bf in RecentUsageModel::refresh() (this=0x555556b0ebe0) at /home/user/kde/src/plasma-workspace/applets/kicker/plugin/recentusagemodel.cpp:542
#18 0x00007fff8a711aa3 in RecentUsageModel::RecentUsageModel(QObject*, RecentUsageModel::IncludeUsage, int) (this=0x555556b0ebe0, parent=0x0, usage=RecentUsageModel::AppsAndDocs, ordering=0)
    at /home/user/kde/src/plasma-workspace/applets/kicker/plugin/recentusagemodel.cpp:123
#19 0x00007fff8a6fc4e1 in QQmlPrivate::QQmlElement<RecentUsageModel>::QQmlElement() (this=0x555556b0ebe0) at /home/user/kde/qt6usr/include/QtQml/qqmlprivate.h:94

kactivities-stats says the following in it's CMakeCache:

//The directory containing a CMake configuration file for Qt6Sql.
Qt6Sql_DIR:PATH=/home/user/kde/qt6usr/lib/cmake/Qt6Sql

Any ideas what the problem might be?