macOS Sequoia 15.1 Does Not Connect to Apple Thunderbolt monitor.

My 2018 MacBook Pro 13 inch also immediately stopped detecting my older Thunderbolt Display after upgrading from Monterrey to Sequoia. I tried many things recommended but none worked. I got it working as follows: My computer has four Thunderbolt 3 ports. I switched the ports between my power input and Thunderbolt display (it uses a Thunderbolt 3 to Thunderbolt 2 adapter. The display came on immediately. Not sure why this worked, but I suspect the port I was using for my Thunderbolt display perhaps had some problem that did not affect it in Monterrey but did affect it in Sequoia. I had used that same port for many years, but now will use the new one. I tried swapping them back to the original ports, but then the Thunderbolt Display again did not work. When I switched back to the "new ports", I again could not get the Thunderbolt Display to work. Finally, it did work when I unplugged the power to the MacBook Pro. Anyway, it is working now. Try switching ports, and you might try unplugging the power to the MacBook briefly and see it that makes a difference. I suspect the power cord might have been a more important factor.

Are you sure you are using the same cables and a configuration that worked before?

Could you possibly restore a backup to a separate partition to see if something hasn't failed in between the upgrades?

Since upgrading to Seqwuoia 15.1 my Apple Thunderbolt Screen has refused to talk to my MacBook Pro.

I have just spent the whole day working with the Apple Support Team and they could not find a work around to get my MacBook Pro 13" M1 2020 to talk to the Apple Thunderbolt screen. Works fine on a Dell Screen but all I get on the Thunderbolt is a black screen. It is hard to make up !!!!!!!

It is ridiculous that a software update makes an Apple Product incompatible with an Apple MacBook Pro.

If any one has a solution please post it here.

Same thing happened to me with an Intel Mac Mini. I have two monitors: an Acer and a thunderbolt monitor. Both worked fine until I upgraded to Sequoia. Afterwards, the audio works from the thunderbolt monitor but not the display.

Unplug display from wall, wait 2 minutes and plug back in. This may reset the monitor.

You could have a bad all in one cable. Run a TB2 cable directly to one of the TB pets on the display bypassing the all in one cabe.

The problem is most certainly a software issue created by Apple that needs to be fixed !!!