Microsoft warned this week that screen sharing in Teams on macOS can fail silently, presenting a black or blank image to meeting participants, stopping mid-session, or refusing to start at all. The root cause, according to a support advisory, is running a version of macOS older than Tahoe 26.4 — an upcoming milestone release that introduces a native sharing fix — combined with low available disk space.

What’s actually breaking

The core symptom is straightforward: you initiate screen sharing during a Teams call, but other attendees see only a black rectangle. Alternatively, the sharing session drops after a few minutes, or the ‘share’ button does nothing. Microsoft confirmed that the bug affects all Macs running macOS builds prior to Tahoe 26.4, and that it’s exacerbated when the startup disk has less than a few gigabytes of free space. The company hasn’t disclosed the precise threshold, but internal testing points to a buffer underrun in the video pipeline when the system can’t allocate temporary storage fast enough.

Crucially, the bug isn’t tied to a specific Teams version. It occurs across all current release channels, including the production, public preview, and GCC-High clouds, because it hinges on a change Apple made to the screen-sharing subsystem in older macOS versions. The Tahoe 26.4 update replaces that subsystem with a new, more resilient framework that Teams can tap into natively.

What this means for you

For everyday Mac users — If you rely on Teams for work calls, client demos, or remote classes, you could be embarrassing yourself without realising it. The black screen may appear only to others; on your end, the sharing thumbnail might still show your live desktop. Microsoft recommends you ask a colleague to confirm what they see the next time you share, or enable the “Show in-meeting notifications” toggle in Teams settings to detect when sharing fails.

For IT admins — You’ll need to accelerate your macOS upgrade cycle if you manage a fleet of Macs. Tahoe 26.4 is required to avoid this issue, and it’s likely your users will start complaining en masse once they encounter it. Additionally, if your organisation uses Government Community Cloud (GCC), GCC-High, or DoD tenants, the same bug applies. Microsoft’s cloud posture doesn’t insulate you from client-side dependencies.

For developers and beta testers — If you’re on Apple’s beta track, the Tahoe 26.4 developer seed already includes the fix. However, if you’re testing Microsoft’s own public preview builds of Teams, note that the workaround below won’t work there — you’ll have to update the OS.

How we got here

The trouble began subtly. In late 2024, isolated reports surfaced on the Microsoft Community forums about black screens during Teams sharing on Macs. Initially, the support team attributed them to VPN conflicts or third-party camera drivers. But as the volume grew, pattern recognition kicked in: nearly every affected machine was low on disk space, and all were running macOS 15.x (Sequoia) or earlier. Microsoft dug into the video pipeline and discovered that the legacy CGDisplayStream API — which Teams used under the hood — would silently drop frames when the system’s I/O buffers filled up. Apple had deprecated that API years ago and moved apps to SCScreenCaptureKit in macOS Tahoe, but Teams hadn’t completed the migration.

The Tahoe 26.4 update landed in Apple’s seed channel in February 2025, bringing a fully documented replacement. Microsoft then issued an internal advisory, which leaked to several enterprise customers before the official KB article went live this week. The company’s engineering team has since confirmed that backporting the fix to older macOS versions isn’t feasible because it depends on kernel extensions that Apple won’t certify for earlier releases.

What to do now

There are two parallel paths, depending on your urgency and update readiness.

Immediate workaround: use Teams’ native sharing tile

If you can’t update the OS right now, Microsoft advises using the “Include computer sound” sharing option — commonly called the native sharing tile — as a temporary fix. This forces Teams to use a different code path that is less susceptible to the buffer underrun. Here’s the step-by-step:

  1. In a Teams call, click Share.
  2. In the tray that appears, select the Window (or Screen) tile — not “PowerPoint Live” or “Whiteboard”.
  3. Toggle on Include computer sound (even if you don’t need audio).
  4. Select the specific window you want to share, and click Share.

This method uses SCScreenCaptureKit where available and avoids the problematic CGDisplayStream path. Microsoft says it reduces black-screen occurrences by over 90% in internal tests, though performance may drop slightly on Intel-based Macs.

Permanent fix: update to macOS Tahoe 26.4

Apple has released Tahoe 26.4 as a stable over-the-air update for all supported Macs. The installation requires:

  • At least 12 GB of free storage for the download and staging
  • A restart (and potentially two, if the firmware updater runs)
  • Up to 45 minutes (Apple Silicon) or 1 hour (Intel)

Before you start, back up with Time Machine. The update can be pulled via System Settings > General > Software Update. If you manage devices through Jamf or Microsoft Intune, test the update on a small ring first — early adopters have reported a minor conflict with firewalls that require a post-update reboot to resolve.

Note for GCC and DoD users — The same Teams client glitch applies. Government tenants use the same underlying video stack; the Tahoe 26.4 requirement is identical. Ensure your compliance team is aware that the update does not change any data sovereignty or endpoint management policies.

If you’re completely stuck

Should neither workaround suffice (e.g., a locked-down enterprise image that can’t be updated for weeks), you can switch to Teams on the web as a stopgap. At teams.microsoft.com, the in-browser screen sharing uses WebRTC and is unaffected by the macOS bug. The trade-off: you’ll lose some meeting controls and the ability to share system audio.

What to watch next

Microsoft has promised to fully deprecate the old CGDisplayStream path in Teams version 2.1 and later, which is expected in early Q3 2025. That means even after updating to Tahoe 26.4, you’ll see a one-time prompt the first time you share after the Teams client update, asking you to grant new screen-capture permissions. Meanwhile, Apple is expected to release a supplementary update (Tahoe 26.4.1) that addresses an unrelated kernel panic caused by some antivirus software — so hold off on bundling that with your Teams fix if your security stack is sensitive.