Lightroom CC Online storage does not work with Mac Catalina 10.15

>The support tech said it was a 'known Catalina issue'.

Adobe tech support has a tendency to just blame your operating system if they can't figure it out. Doesn't matter what your OS is but they will definetly do this if you are at the very latest updates. In this case this is NOT a known Catalina issue. The only known issues are listed here: https://helpx.adobe.com/lightroom-cc/kb/macos-catalina-compatibility.html . It is indeed an issue if you are behind a commercial firewall at a workplace. Typical commercial firewall configurations block the ports that Lightroom uses.  It is extremely rare to see this in a home environment and the standard built-in firewalls in Mac OS X and in Windows will not cause problems for Lightroom Cloudy. Perhaps if you have some commercial firewall software installed (don't do that they are without exception terrible!) the problem could be due to that. It can also cause problems if your home router is locked down more than typical or if your ISP filters traffic. But typically you wouldn't see intermittent connectivity. It simply wouldn't work at all. Another common problem in home setups that might cause problems is double NAT. For example, you have a modem from your ISP that does network address translation and firewall duties and you have your own wireless router that also does NAT. In cases like that you want to turn off NAT (i.e. put it in bridge mode) on one of them so that you only have one layer of NAT. Also, generally if your router and ISP supports it, you should enable ipv6 but I am pretty sure Lightroom Cloudy will work without it. 

As far as I know there is no issue with Lightroom (the desktop version of the cloud version of Lightroom) and Catalina that would prevent it from working correctly which means that the problem is in the network connection, either on the computer, your router config, or on the ISP side. 

>Are you on the CC version or the desktop version?

This is Lightroom (the cloud version) running on Mac OS X Catalina.

> FWIW my Speedtest results show 5ms pings and 0.85ms Jitter..40 Mbps up

The speedtest test is good but you want to check prolonged pinging in network utility as I described to see if you have any intermittency. The speedtest check is often too short in duration to catch that. It also doesn't catch issues where your ISP's connection to the outside world is bad. Or where their DNS is not working correctly (very common nowadays). Do the ping to an Adobe server and run it for a few minutes and see if your ping is constant.

I have no issues like you describe on a fairly standard home internet connection. Plain Catalina install and LR 3.

If you see disconnects like you describe I would suspect networking issues. Simplest test is doing a ping test in network utility (just type it in the looking glass), type something like www.adobe.com as the host and set it for unlimited pings. You should get consistent numbers of about 15 to 30 milliseconds on most internet connections. If you see much higher numbers, see it fluctuate wildly or even drop pings once in a while, you have networking issues. Could be many different causes. You can also try installing the speedtest app from the apple store and see if your internet speeds, ping times (should be lower even than the 15 ms above as it pings a much closer server) are consistent or fluctuate terribly.