Catalina: instead of fix, package contained chime
There's a "Security Update 2020-001" for Catalina that just came out.
I'll cut to the chase: it didn't help one bit. The machine dies exactly as before, per the reproduction instructions. It's incredibly easy to do. I can crash it at will. If not for the Twilight Zone screwing up the entire world, I probably would have gone into an Apple Store and done it on their demo hardware by now.
All I wanted was a machine that worked as advertised.
I should note that Apple has a history of doing non-security things in these patches. They're getting as bad as a certain other infamously sucky OS vendor in the consumer space.
Case in point: almost a year ago, they came out with a "Security Update 2020-002" for Mojave, which was the version before Catalina. Despite the name, it did something crazy to the Intel graphics stuff that some machines had, and those machines started hanging/freezing, crashing, and just generally being unusable.
They then silently fixed it in "Security Update 2020-003" for Mojave.
Ironically enough, *that* stupidity is what forced me to buy the 2020 MacBook Air as a replacement, and that is where I am now hitting this Thunderbolt issue.
It has not been a good year for this stuff. I am honestly considering migrating everything back to the MBP and then loading the MBA into a trebuchet and aiming in the general direction of Cupertino. It might actually make a dent.
"Security", indeed. I wanted working Thunderbolt. They gave me a chime. Yes, that's right, the latest Catalina "Security Update" turns the (in)famous Mac chime back on.
At least they have their priorities straight. Can't have the machines booting up without a chime, can we.
You're going to hear that chime a LOT. Every time you kill it by hotplugging a Thunderbolt device.