Cannot Screen Mirror in Tahoe

I've tried lots of suggested routes for sorting this out, but nothing deals with the basic fact that the screen mirroring button no longer has any functionality. Clicking on Screen Mirroring merely closes it down.

The Mac does not rely on Windows-like side-loaded "Drivers" which are actually packages of resolutions and settings for a specific display. Instead, it goes straight to the immutable source -- it asks the display itself.

To get a Mac display to become active, you need the Mac to query the display, and the display to answer with its name and capabilities. Otherwise, the display will not be shown as present, and no data will be sent to the display. "No signal detected" is generated by the DISPLAY, not by the Mac.

This query is only sent at certain times:

• at startup

• at wake from sleep — so momentarily sleeping and waking your Mac may work

• at insertion of the Mac-end of the display-cable, provided everything on that cable is ready-to-go

• hold the Option key while you click on the (Detect Display) button that will appear in Displays preferences (from another display)

so try doing some of those things and see if the display comes alive.

Modern Displays with multiple ports are sometimes busy scanning the other ports, looking for an input, and miss the query from the Mac. They need to pay attention to the port you are actually using, or they will miss the query.

Some displays have On-Screen Display settings that can be used to tell the display a computer is attached on a certain port, or a certain port should be highest priority. Changing those may make your display more responsive.

see if this article form TCL has any additional insights:

https://support.tcl.com/apple-airplay-homekit-rokutv-setup

if not, you may have to use a high-end HDMI cable, certified at least PREMIUM high speed.

This isn’t a any normal AirPlay break, it’s almost certainly a protocol mismatch introduced in Tahoe. macOS only shows AirPlay receivers that respond correctly to its newer discovery handshake, and a lot of TCL TVs rely on an older AirPlay stack that still works fine with iOS but fails macOS discovery after an OS update. That’s why your iPhone still mirrors and the Mac doesn’t even list the TV.

For fixes, the only things that actually help are on the TV side, update the TCL firmware manually (don’t assume auto-update ran), fully power-cycle it by unplugging for a minute, then re-enable AirPlay in the TV settings so it re-advertises itself on the network. Also make sure the TV and Mac are on the exact same subnet, Tahoe is stricter about Bonjour discovery and will silently hide devices across VLANs or guest Wi-Fi, which office networks often use.

If none of that brings it back, it’s not something you can fix on the Mac, Tahoe changed AirPlay requirements, and until TCL updates their AirPlay implementation, HDMI or an Apple TV is the only reliable workaround.

am I interpreting this statement correctly?

<< [current, i.e., Tahoe and subsequent ] MacOS only shows AirPlay receivers that respond correctly to its newer discovery handshake. >>

If so, this might have impact for a LOT of older AirPlay emulations on non-Apple devices, including Sony TV sets.

Try to go to /library/Preferences, delete a file called "com.apple.windowserver.plist" (something between those lines), shutdown, start your computer again, and it will show up. Force detect new displays if needed.