Wow. I have just fixed this, completely by accident, after checking for driver updates through Dell Command. It said "we're unable to check for updates because you need to restart to install previous updates" I have restarted my laptop any number of times over the last 3 weeks... but it seems I actually needed to click the "restart" button in Dell Command to finish the update process. Just putting this here in case anyone has the same issue.
I have a Dell WD19 dock at home, connected via USB-C to a Dell Latitude 5530 laptop, with an external Dell 24" monitor connected to the dock via DP cable. This setup has been working fine for a couple of years with 3 different laptops, 2x Dell and 1x HP, and I've never had any issues connecting to docks or external monitors previously. Recently, the laptop stopped recognising the external monitor. (I think this coincided with driver/firmware/BIOS updates via Dell Command.) I've tried disconnecting/reconnecting cables, and power cycling various ways, but nothing has worked. Display Options now shows the laptop screen (1) and a greyed out second monitor (2), with usual options to "extend/duplicate" to 2 along with "only on 2", but when you select those options, it reverts to laptop screen only. I've tested the laptop on a different WD19 at the office, and that works fine (although I had to power cycle that dock). I've tested the connection directly from laptop to monitor via HDMI -- that works fine. I've tested the dock setup at home with a different Lenovo laptop, and that works fine with the dock & second monitor via DP. I know that Windows 11 offers to remember the setup you had at a particular dock that you've used previously -- down side being that you have to do this every single time if you're hotdesking. So the behaviour I'm seeing is that the Latitude laptop has "misremembered" the config for this specific combination of dock & monitor, and is not letting me change it. Is there a way to reset these settings? Either easily within Windows settings or the long way around, by uninstalling/reinstalling drivers?
WD19 Dock not recognising monitor