Hi,
I've got an issue with both the thunderbolt2 ports on my iMac (Retina 5K, 27-inch, Late 2015 Running Catalina. (Model 17,1)
I have an OWC Thunderbolt 2 hard drive dock that isn't connecting to the iMac over thunderbolt 2. It can connect via USB3.0, but it is much slower and isn't able to...
I just tried installing an Apple software update for the Thunderbolt port and it has frozen my 2015 iMac while restarting (wheel has been spinning for more than 10 minutes now).
I don't like to force a shutdown during a firmware update but might have to do it in this case.
My advice - don't...