After latest Catalina update, apps extremely slow to launch when computer is online

After waiting still longer for my new account to log out, I decided to give up. I held down the fingerprint button, thinking that would force the machine to power down, but instead it switched me back to my other account. Okay? Clicking my name in the menubar, I saw that the new account was still logged in. I restarted the machine (which required username and password since there was another account logged in). After restarting, all is well, problem solved, everything launches as expected even when the internet is turned on.

So I don't know what in that process fixed the problem--I'd tried restarting several times before and it didn't help. But maybe someone who knows more about these things can hazard a guess. Or, try forcing a restart when two accounts are logged in and see if that somehow fixes the problem for you too?

Just as a followup... I found a thread with a similar problem which suggested creating a new admin account and seeing if the newly created account has the same problem. So I tried that. tldr a new account has the same problems and then some...

After creating a new account I switched to it from the menubar (without logging out of my normal account). There was the laborious setup process before the account would log in, as normal. But then the Finder took an extremely long time to launch. For several minutes, I saw the standard Catalina backround picture and the dock, with no menubar, and the computer was totally unresponsive. When the Finder finally launched, I was able to get a window open and tried launching BBEdit (which normally opens pretty much instantly). It took 28 bounces (I counted) before the dot appeared under the icon in the dock. Then there was a spinning rainbow for maybe 10 seconds, and I finally saw a text window. Quitting also resulted in a spinning rainbow, though not for as long. Launching again was the same as the first time. Then I made the colossal mistake of logging out. It's been ~15 minutes so far, it looks like it looked before the Finder launched. I can move the mouse around, but that's it. This newly created account is stuck in the middle of logging off.

(I'm on a different Mac now, running 15.6 instead of 15.7, and it's fine.)

One way to test this might be to add it to your hosts file (in /etc/hosts) mapping it to 127.0.0.1. That should prevent your computer from connecting to that server. (I'm not recommending this, since I don't know what that server is for or whether blocking it would solve the problem. Just saying a way it could be done.)