diff -Naur a/3rdparty/qwtplot3d/CMakeLists.txt b/3rdparty/qwtplot3d/CMakeLists.txt
--- a/3rdparty/qwtplot3d/CMakeLists.txt	2021-08-28 17:44:11.000000000 -0400
+++ b/3rdparty/qwtplot3d/CMakeLists.txt	2026-05-23 17:02:31.235163815 -0400
@@ -31,13 +31,8 @@
   add_compile_definitions( GL_SILENCE_DEPRECATION )
 endif()
 
-find_package(Qt6 COMPONENTS Core Gui OpenGLWidgets QUIET )
-if( Qt6_FOUND )
-  set( QT_VERSION_MAJOR 6 )
-else()
-  find_package(Qt5 COMPONENTS Core Gui OpenGL REQUIRED )
-  set( QT_VERSION_MAJOR 5 )
-endif()
+find_package(Qt5 COMPONENTS Core Gui OpenGL REQUIRED )
+set( QT_VERSION_MAJOR 5 )
 
 find_package( OpenGL COMPONENTS OpenGL REQUIRED )