A high-precision measurement of the 1s₁/₂2p₃/₂J=2 → 1s₁/₂2s₁/₂J=1 intrashell transition in He-like uranium (Z=92) has been performed, achieving an accuracy of 37 ppm. This experiment uses a multi-reference method based on Doppler-tuned X-ray emission from stored relativistic uranium ions with different charge states. The energy of the transition is determined with high precision, enabling the testing of higher-order QED effects and electron-electron interactions in the high-Z regime. The results allow for the separation of one-electron and many-electron QED effects, as well as the comparison of different theoretical approaches. The experiment is conducted at the ESR storage ring, where uranium ions are stored, cooled, and decelerated. The transition X-rays are detected using two high-resolution crystal spectrometers placed at observation angles of ±90°. The energy of the transition is measured with respect to analogous transitions in Li-like and Be-like uranium ions, enabling the disentanglement of one-electron and many-electron QED effects. The results are in good agreement with the most recent ab initio QED calculations but do not agree with predictions based on relativistic many-body perturbation theory and RCI methods. The experiment provides a benchmark for calculations in the strong-field domain and highlights the importance of high-precision measurements for testing QED in extreme fields. The results demonstrate the potential of Doppler-tuned X-ray spectroscopy for testing fundamental physics in extreme conditions.A high-precision measurement of the 1s₁/₂2p₃/₂J=2 → 1s₁/₂2s₁/₂J=1 intrashell transition in He-like uranium (Z=92) has been performed, achieving an accuracy of 37 ppm. This experiment uses a multi-reference method based on Doppler-tuned X-ray emission from stored relativistic uranium ions with different charge states. The energy of the transition is determined with high precision, enabling the testing of higher-order QED effects and electron-electron interactions in the high-Z regime. The results allow for the separation of one-electron and many-electron QED effects, as well as the comparison of different theoretical approaches. The experiment is conducted at the ESR storage ring, where uranium ions are stored, cooled, and decelerated. The transition X-rays are detected using two high-resolution crystal spectrometers placed at observation angles of ±90°. The energy of the transition is measured with respect to analogous transitions in Li-like and Be-like uranium ions, enabling the disentanglement of one-electron and many-electron QED effects. The results are in good agreement with the most recent ab initio QED calculations but do not agree with predictions based on relativistic many-body perturbation theory and RCI methods. The experiment provides a benchmark for calculations in the strong-field domain and highlights the importance of high-precision measurements for testing QED in extreme fields. The results demonstrate the potential of Doppler-tuned X-ray spectroscopy for testing fundamental physics in extreme conditions.