Basic starting point for me is what you’re actually running, which requires details of your software stack’, ie. what release are you using, and if using a release that has backports available (eg. 22.04 LTS), if you’ve added that to get a newer LXQt version. You’ve not provided any release details.
I’ve looked at the video, and sorry I don’t see what you’re actually asking about… I notice the pointer move, as well as camera angle change, but I gather that’s not what you’re asking us to look at. If there is something you see in that video, giving us the time in the video where it happens, and telling us where to look may help (you mention white line pops up at the bottom, but all I saw I assumed related to movement of the camera).
(FYI: If it’s a LTS release, as there are kernel stack choices, with the default set by your installation media, giving that detail may also be helpful if related to kernel modules (aka drivers) too… for older hardware I’ve often found the older kernel stack (GA) performs better, just as newer hardware tends to do better with newer kernel stack (HWE))