Non-web user interface not working with 6.40

[theoreticMK]

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Description

I just compiled ROOT from source in the same way as for previous versions.
My CMake command:
cmake .. -DCMAKE_INSTALL_PREFIX=/opt/root6 -DCMAKE_CXX_STANDARD=23 -Dbuiltin_xrootd=ON -Dxrootd=ON -Droot7=ON -Dhttp=ON -Dunuran=ON -Dvdt=ON -Dbuiltin_vdt=ON -Dqt6web=ON -Dbuiltin_ftgl=ON`

While the web interface seems to work OK, using the standard one (root --web=off) does not.
See commands and their results below. TCanvas is not created, TEvenManager::Create fails, and TBrowser segfaults.

   ------------------------------------------------------------------
  | Welcome to ROOT 6.40.01                        https://root.cern |
  | (c) 1995-2025, The ROOT Team; conception: R. Brun, F. Rademakers |
  | Built for linuxx8664gcc on May 27 2026, 09:29:50                 |
  | From heads/v6-40-00-patches@v6-40-00-13-g151f4ff7bc3             |
  | With c++ (Debian 14.2.0-19) 14.2.0 std202302                     |
  | Try '.help'/'.?', '.demo', '.license', '.credits', '.quit'/'.q'  |
   ------------------------------------------------------------------

root [0] new TCanvas
Warning in <TCanvas::ResizePad>: gPad has at least one zero dimension.
(TCanvas *) 0x563d8beeb6c0
root [1] TEveManager::Create()
Error in <TRint::HandleTermInput()>: TEveException caught: TEveManager::Create window system not initialized.
root [2] new TBrowser

 *** Break *** segmentation violation
...
===========================================================
#8  0x00007f8675801750 in TGClient::GetDefaultRoot() const () from /opt/root6_40/lib/libGui.so
#9  0x00007f867595ff2c in TRootBrowser::TRootBrowser(TBrowser*, char const*, unsigned int, unsigned int, char const*, bool) () from /opt/root6_40/lib/libGui.so
#10 0x00007f867596022c in TRootBrowser::NewBrowser(TBrowser*, char const*, unsigned int, unsigned int, char const*) () from /opt/root6_40/lib/libGui.so
#11 0x00007f868f70223e in ?? ()
#12 0x00007ffe323b34f0 in ?? ()
#13 0x00007ffe323b34e8 in ?? ()
#14 0x00007f8699cad1f0 in ?? () from /opt/root6_40/lib/libCore.so
#15 0x00007f86926e49e8 in ?? () from /opt/root6_40/lib/libCling.so
#16 0x00000005926e4e7c in ?? ()
#17 0x00007ffe323b34f0 in ?? ()
#18 0x0000000000000001 in ?? ()
#19 0x00007ffe323b34e8 in ?? ()
#20 0x00007f868f701088 in ?? ()
#21 0x0000000000000001 in ?? ()
#22 0x00007f8699aa1b49 in long TPluginHandler::ExecPluginImpl<TBrowser*, char const*, unsigned int, unsigned int, char const*>(TBrowser* const&, char const* const&, unsigned int const&, unsigned int const&, char const* const&) () from /opt/root6_40/lib/libCore.so
#23 0x00007f8699aa0d07 in TGuiFactory::CreateBrowserImp(TBrowser*, char const*, unsigned int, unsigned int, char const*) () from /opt/root6_40/lib/libCore.so
#24 0x00007f8699a9d41c in TBrowser::TBrowser(char const*, char const*, TBrowserImp*, char const*) () from /opt/root6_40/lib/libCore.so
#25 0x00007f8698fbf090 in ?? ()
#26 0x00007ffe323b3610 in ?? ()
#27 0x0000563d8ac44600 in ?? ()
#28 0x00007ffe323b3b80 in ?? ()
#29 0x00007f869278bf60 in ?? () from /opt/root6_40/lib/libCling.so
#30 0x00007f86928065a4 in ?? () from /opt/root6_40/lib/libCling.so
#31 0x00007f8692784396 in ?? () from /opt/root6_40/lib/libCling.so
#32 0x00007f8692785cb8 in ?? () from /opt/root6_40/lib/libCling.so
#33 0x00007f8692785e9c in ?? () from /opt/root6_40/lib/libCling.so
#34 0x00007f8692877687 in ?? () from /opt/root6_40/lib/libCling.so
#35 0x00007f869265603a in ?? () from /opt/root6_40/lib/libCling.so
#36 0x00007f869267966b in ?? () from /opt/root6_40/lib/libCling.so
===========================================================

The same setup and commands worked fine for 6.38.

Reproducer

Run root with --web=off and try to create TCanvas, TEveManager::Create or TBrowser

ROOT version

6.40.01

Installation method

build from source

Operating system

Debian GNU/Linux 13 (trixie)

Additional context

No response