Second monitor does not stay connected

[stevecoh1]

I originally posted this on Unix and Linux stack exchange but it's looking more and more like a possible Kubuntu-specfic issue so I'm repeating it here.

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I suspect this is a Linux question but it might be a Hardware question.

I have a new Lenovo Thinkpad P16 Gen2 laptop. A very nice machine, it came with Ubuntu Linux installed. I am running Kubuntu 24.04.1.

I also have a 10-year old Lenovo Thinkpad T540p. It runs Ubuntu 24.04.1.

With the older laptop, connecting the second monitor is noticed immediately by the system. This is handy because I sometimes move around the house with it. Whenever the second monitor is plugged in, it is noticed.

With the newer laptop, if I unhook the monitor and then return and plug it in, it isn't noticed. I have to reboot the machine to get the second monitor to come up.

I suspect it's probably a Linux issue, but I don't have a Windows dual boot set up with which I could confirm this. Can someone suggest a way to diagnose the problem?

Update:
1. my original post was inaccurate. I do not need to unplug the monitor for the connection to to the second monitor to go away. Just letting it sit idle makes it go away.

2. trying the

udevadm monitor

command that someone suggested did nothing. No output was generated on either plugging or unplugging the monitor.

3. A notification from KDE (remember I am running kubuntu) popped up briefly and seemed like it might be relevant but it disappeared before I could finish reading it. Secondary question: notifications pop up for like five seconds and then disappear. How can I SEE them? Are they stored anywhere?

[Princey]

I can't answer the 1st question as I can't remember when last I used dual monitor set up. However, your notifications duration can be changed and can be read even when they disappear. Assuming you did not disable the notification icon in the system tray, if you left click on the notification icon (sometimes it's hidden and you might have to click the triangular-like arrow before the time as shown in the screen shot. Left clicking on the notification icon (says notifications) will bring up the notifications history, right clicking will bring up the configuration menu where you can specify how each application's use of notifications is handled. You can even edit the duration the notification badge (popup) stays active.

[oshunluvr]

The first question I would have is does this happen with another distro? A LiveUSB bootup might answer that.

My second question is what does the output of dmesg say with regards to video or screen?

What is sounds like to me is that powerdevil or some other system program is turning off the second video port to save power.

Open up Konsole and type this:

find /sys/devices -name "edid"

then wait until the monitors goes off and won't come back on and do it again. Post the output from both.

[oshunluvr]

Also, it the very least your should include you video card(s) models and the monitor model.