Could somebody please either let me know (or test) how sidecar works with an iPad and an external display?
I have a Mac mini M1 with two desktop monitors connected. I also use an iPad Air 4 (A14 chip) on my desk hooked up to a USB-C monitor (monitor #3). The iPad will only mirror its display to the monitor #3 because it doesn’t have full external display support. Therefore, monitor #3 only has the center ~4:3 area filled with content and black bars on the side. So be it, it’s sort of like having 3 monitors. I can either use apps like Apple Notes on the iPad (also #3), or use sidecar from macOS and have 3 displays (of a kind) simultaneously on my mac mini.
However, the M1 and above iPads support extended external displays, rather than just mirrored. So how does that work with sidecar on the iPad?
Does it force mirroring, but then use the resolution of the iPad with black bars on the monitor?
Or force mirroring but use the resolution of the #3 external monitor, and have black bars on the iPad?
Or let you use the sidecar “app” on either display and a different app on the other display? Could this option mean that I can use sidecar for putting macOS windows onto display #3, and still use the iPad for writing on a PDF in an iPad app simultaneously?
I’m not entirely clear what you are looking to do. Let me start here — I think you very well understand this from how I read your post. I just want to make sure we are singing from the same songbook. There are two different external display options you have when it comes to pairing your iPad and Mac. One is Sidecar, which you mention. The other is iPad secondary display support. Sidecar expands your Mac. It makes your iPad work like another macOS monitor. Secondary display support expands your iPad with a secondary screen.
What it seems you are asking about, if I’m reading this right, is how to make sure when using your external display to extend your iPad how to turn off mirroring mode in favor of Stage Manager.
When you plug your iPad into an external display, if the iPad detects both a keyboard and a mouse, it will automatically enter Stage Manager. If not, it will automatically enter mirroring mode. You will get a notification at the top of the iPad screen indicating which mode it chose. If you catch it, you can click that and change the mode as you see fit. If not, you can go to settings and change it manually.
I was forever having to switch modes when I would connect to my external display because I have a Bluetooth keyboard and mouse. Those were not active before I plugged in my iPad, so the iPad wouldn’t detect them and would go into mirroring mode. I switched my set up so that my keyboard is active when I plug-in, and now I’m always immediately in stage manager.
On the “display look” question, for me when using Stage Manager, the entire iPad desktop/home screen fills the display.
It sounds like you’re hoping you can have sidecar operate through your iPad and the external display at the same time. It does not work that way, though. You can have your iPad driving the secondary display, or you can have your Mac driving the iPad through sidecar (but the external display won’t be running sidecar; it will just turn off). You could, however, use Universal Control to control your iPad connected to the external display. Then you’ d have your Mac screen, your iPad screen (running iPadOS), and your external display running iPadOS.