My external monitor shows a blue screen after update to 10.15

A temporary workaround I found was switching the dongle I used for connecting to the external display. I had an extra Dell hockey puck, and that seems to have fixed the issue (HDMI -> USB-C). Likely an Apple dongle would do the same thing.

I checked in Apple store some time ago when my charger stopped working. Extra screen works via Apple HDMI adapter but I didn't want be ripped off so I searched on the internet and you simply need to buy an adapter that is compatible with Catalina 10.15. It should say so in the product description. I got myself an adapter from Amazon, brand QGeeM - works perfectly and cost me only £15.

You could try installing the Catalina Displayport USB driver (do a web search), though it is still beta. Fixed my issue.

edit: here's a link: https://www.displaylink.com/downloads/macos

I had this problem but The adapter manufacturer Startech made me a change for a new one and the problem has ended, it was a faulty piece.

Sounds like a HDMI handshaking issue. If you have the ability to use a DisplayPort connection, handshaking won't be an issue.

For what it is worth, I am seeing this behavior when connecting from my MacBook Pro to an OWC Thunderbolt 3 Dock. I have two HP VH240a monitors that are connecting via HDMI dongles, one converting to Mini Display, one to USB-C. Mini Display works fine, USB-C shows the same blue screen behavior as indicated previously.

Took the dock out of the equation and saw the same behavior. I'm guessing something to do with the signal on the conversion, passive versus active whatnots.

You could try installing the Catalina Displayport USB driver (do a web search), though it is still beta. Fixed my issue.

edit: here's a link: https://www.displaylink.com/downloads/macos

This fixed my monitor, I'm using a startech USB-C dongle, and my screen no longer goes blue when I plug it in. Thank you!

edit: Worked until I unplugged the dongle and replugged it in, it no longer works and I'm back to a blue screen.

I have the same problem, I use a Startech USB-C to HDMI Converter when I plug it works for 2-3 seconds then blue screen.

I also have a Dell USB-C Docking Station and it works fine with HDMI I don't know why!

Same problem here on brand new MacBook Pro 16” at work. Reset SMC and NVRAM multiple time in desperation. Tried multiple HDMI adapters. As others have stated projector works fine for around 5 seconds, then blue screen. Gave to IT guy for afternoon, unable to resolve it, others in company having same problem. At work for meetings, have two copy presentation to $300 Surface to present. Beyond annoying, well beyond.

Same problem here on my iMac pro 2017. I've got the newest version of Catalina 10.15 and am trying to connect my external display via an icy-box usb-c to hdmi adapter. Before the update, everything worked fine in Mojave. Now it will show the image for a couple of seconds, then it turns to a blue screen on the external display.

Hi

Exactly same problem,when connected my MacPro to Sony projector 4k blu screen flash every few seconds makes watching anything impossible.When connect through Yamaha soundbar with HDMI after few seconds constant blue screen.

No help on forums.Catalina sucks.

Has anyone found a fix? I am using a DELL USB-C to HDMI adapter which has nothing to do with DisplayLink and has worked perfectly fine until updating to Catalina. Under BootCamp it works fine too, without installing any drivers. Thanks.