Sorry, the placeholder slipped through — the bug is FB24054098. The attached sysdiagnose was captured with both Studio Display XDR units connected, one lit and one dark. Thanks for the clarification on the spec reading. Understood that the XDR falls under the single-display line because of its 120Hz maximum, even when set to 60Hz.

Same failure here on a 14" MacBook Pro M4 Pro (Mac16,8), but with two Apple Studio Display XDR rather than third-party monitors. Both on display firmware 26.4, both connected directly to Thunderbolt ports with Apple cables. Only one ever lights up. The second does not appear in Displays settings at all, although System Information lists it as an online Thunderbolt device with correct model and firmware. Forcing 60 Hz on all displays, reversing connection order, cold boot with both attached, and daisy-chaining make no difference. Filed as FB[deine Nummer], with a sysdiagnose captured while both displays were connected – one lit, one dark. That is the capture configuration that was missing from the earlier reports in this thread. Posting the number here as requested. Worth noting this is two Apple displays on an Apple Mac, within the published specification of two external displays up to 6K at 60 Hz.