The MB Pro stays on long enough to complete the First Aid test in Disk Utility, without finding a problem.The MacBooks started up in Target mode are not visible in Disk Utility either, so they are not just sitting there unmounted.However, it does not show anything as connected to the ports when either MacBook is connected. Note that the Thunderbolt port shows as existing when I look at the system report in About This Mac. To check that the problem is not with the iMac, I started the MB Pro in Target Disk mode while connected to the MacBook Air using a USB-C cable.No encryption and no firmware password anywhere.Both are on the same current Monterey version. The MacBook Air does not show up on the iMac when booted in Target mode. Suspecting that the problem might be with the MB Pro, I booted my wife's 2021 MacBook Air and connected it to the iMac the same way, just to see what would happen.I don't know whether or not that matters. This shows no IP address on the iMac end.

I have also looked in the network locations, and at the Thunderbolt Bridge configuration. When connected, which I do before booting the MacBook, it does not show up in Finder or the desktop on the iMac.The MB Pro is also on Monterey, though not the latest version as it won't stay on long enough to update it.

I have therefore bought the Apple T3 to T2 adaptor and an Apple T2 cable this morning to connect the two computers. The iMac has Thunderbolt 2 ports and the MacBook Pro has Thunderbolt 3 ports. I am using my Late 2015 27' iMac for this.

I don't have a Time Machine backup for the Pro and want to recover the files before sending the MacBook Pro for repair.

It stays on indefinitely when I start it up in Target Disk mode, no matter which of the two ways I use to start the Target disk mode.

It does boot correctly to that point and is fully usable while alive for three minutes.

Touch bar does not work, and it reports a Panic crash after 180 seconds of not receiving input from the Touch Bar (dfrd read). Core issue is a 2019 16' MacBook Pro that has had a coffee spill.Here is the situation and what I have tried so far: I have read at least 20 posts on this in various forums without finding a solution.

Thunderbolt 3 target disk mode