sidecar unable to connect deviced timed out I have been trying to use Sidecar in the public betas of macOS Catalina and iPadOS 13.

I have a 2019 Macbook Pro, and a 3rd generation iPad Pro, so I know I have supported devices.

Both devices are on the same Wifi network, and both have Bluetooth enabled.

Both devices are logged into iCloud with the same AppleID.

Both devices have two-factor authentication enabled.

I have tried this both with and without a USB-C cable connection between the two devices.

The Sidecar preference pane in System Preferences does appear, and when I go into it I can see in the "Select Device" dropdown that my Mac can "see" my iPad Pro.

However, when I try to connect to it, I get the following after a pause:



I keep watching this page for troubleshooting tips, but none have been useful for me thus far.

FWIW, I have been a "good citizen" and reported my problems to Apple via the Feedback Assistant apps on both devices, so in case this is a temporary bug, I've reported it.  I'm just asking here in case someone else has encountered this issue.

Edit: Eventually, Sidecar started working for me (sometimes) after some of the later public betas came out.  I'm not sure exactly which version(s) of Catalina and/or iPadOS made the difference for me.  So far it has worked without any timeouts in the final versions. I didn't need to downgrade and then re-upgrade as the submitted answer suggests, although I'm glad that has worked for some.
I had this problem setting up a new computer. For me, what fixed it was going into Settings &gt; Accounts &gt; iCloud and checking KeyChain

It said I needed to update my account security and prompted me with a few security questions. This seems to have indirectly solved the problem; perhaps some minimum standard of security was not upheld and was causing quiet failure.

Unfortunately, I'm guessing that this won't solve everyone's problems as it seems to be a pretty generic message as mentioned above, just thought I'd add my solution to the pile for everyone who's going down the list and trying everything.