Curious Cable Question

[MacInWin]

Nah, dumb luck. I will say that I tend to stay close to the Apple Ecosystem--my TB dock is from Belkin, I use an Apple Thunderbolt Display for an external monitor. I don't use too much exotic software, mostly mainstream (Office, Photoshop, stuff from the App Store) or very reliable (OnyX, DetectX Swift, etc). And I was cautious about jumping to Catalina. I have one 32-bit app that now has in hand the 64-bit driver they needed from the hardware vendor to update their application for scanning slides and promises an update soon. In the meantime, I'm not scanning slides. Most of the "hard" issues I've seen with Catalina have involved hardware/software that is a little more rare than anything I do. And I am willing to spend a bit more for cables/adapters from companies whose name and quality I trust.

[krs]

From what I have read, this seems to be the best TB3 to DVI cable there is right now. Works with displays where others didn't - they are also the only company so far that actually specifies the chip set they use.USB-C to DVI Adapter Cable - 6.6 ft. / 2 m - USB-C Video Adapters | StarTech.com Canada

However, as they say, the proof is in the pudding.
If you want to try it, make sure you get it from a place where you can return it if it doesn't work.
Amazon.com has it and I think you can return it postage-free if it does not work.

[kitjv26]

What is in System Preferences/Dispays? When you get there, does a separate box open on both the iMac and the external? on the Arrangement tab, do you see both displays?

Yes, there is a separate box on the iMac & the external display. And on the Arrangement tab, both displays are indicated.

- - - Updated - - -

What does it show if you look under Apple Menu > About This Mac > System Report > Graphics/Displays?

Under Graphics/Displays, both displays are there.

[kitjv26]

I think that I concur with krs regarding finding a cable that is compatible with both my iMac & Catalina. The idea of rebooting the external display & waiting until it decides to return to life is only acceptable until I find a permanent solution.

Thank you all for your input. I truly appreciate it.

[kitjv26]

From what I have read, this seems to be the best TB3 to DVI cable there is right now. Works with displays where others didn't - they are also the only company so far that actually specifies the chip set they use.USB-C to DVI Adapter Cable - 6.6 ft. / 2 m - USB-C Video Adapters | StarTech.com Canada

However, as they say, the proof is in the pudding.
If you want to try it, make sure you get it from a place where you can return it if it doesn't work.
Amazon.com has it and I think you can return it postage-free if it does not work.

Thank you for the heads-up! Will follow through.

[krs]

Yes, there is a separate box on the iMac & the external display. And on the Arrangement tab, both displays are indicated.

Under Graphics/Displays, both displays are there.

I assume in both these cases the external display is actually working - or is it?

[kitjv26]

I assume in both these cases the external display is actually working - or is it?

Indeed it is!

[MacInWin]

Next time it ISN'T working, look at those System Preferences to see if the monitor is there in that case. Could be useful information for troubleshooting.