The fact that you can ask for help and someone can actually help is why I finally decamped from Microsoft/Apple into Linux.
I get bugs like this from Apple/Microsoft products all the time. The only difference is that I have no ability to fix them, and I have to hope that enough other people have the same bug to make it important enough to fix.
I see it the other way around. If I have a fresh install of Ubuntu 22.04 on a new laptop, with no other OS installed and everything freezes when I connect to my monitor with the laptop open (so that the built-in display is active), I’d uninstall Ubuntu and be done with it.
In fact, after I had given my parents an Ubuntu laptop and the OS upgrade to the next stock Ubuntu major version hosed the laptop on two occasions to the point that I had to scour forums for hours for advice and hope to get the thing to boot into the GUI again, I handed them my MacBook Pro 13". Which is still in use after almost 10 years and works flawlessly!
> Which is still in use after almost 10 years and works flawlessly!
You are comparing macOS 10 years ago against Ubuntu 10 years ago.
While most Linux systems have gotten better over 10 years, macOS and Windows have degraded over 10 years.
Edit: I may have misread your message. You may have handed them your 10 year old macOS machine today. Nevertheless, my statements below still hold.
My Bluetooth works better on Linux than on Windows or macOS. My Thunderbolt hubs work better on Linux than on macOS. Graphics is a mixed bag--Windows clearly wins here with macOS and Linux being equally quirky and weird (for me macOS regularly loses the ability to play videos on webpages forcing a full reboot and Linux often winds up clearly using software and heating up the CPU).
Granted, I'm not using NoName(tm) laptops for Linux. I'm making sure to use something like a Lenovo Carbon X1. However, if we're comparing to macOS, I think that's a fair comparison point.
> Interestingly, when I run "Try Ubuntu" from the bootable USB device, I can connect the monitor and have Ubuntu working on both screens. It seems that, somehow, the problem is with the installed OS, rather than the OS itself.
Frustrating. But this part seems like a hint that figuring out the issue won't take too much longer with some investigation.
A friend of mine has had issues using an external DP-connected monitor when running installed Fedora, but it works from the Fedora live environment. I suppose it's related?
I get bugs like this from Apple/Microsoft products all the time. The only difference is that I have no ability to fix them, and I have to hope that enough other people have the same bug to make it important enough to fix.