Plus, TB3 is supposed to be good for two displays running I'm only driving two displays at so nowhere near the limit of the dock. AFAIK with Thunderbolt 3, the display traffic is dedicated and effectively separate from anything else going down the TB3 cable. the dock is a proper Thunderbolt 3 dock, specifically a WD19TB from Dell (and yes, it's running the current dock firmware, v01.00.14.01 / A03, and the laptop also has all the latest BIOS/drivers/etc). Re: pipeline / bandwidth - also a decent thought, but the dual monitors on the dock should *not* be enough to kill it. No way to change framerate, at least not with Zoom. The flickering seems to be lessened when not using "HD," but it does still happen (at least based on what I can see from looking at the preview window while playing with Zoom right now).
Reso/framerate good thoughts, but the only options (at least with Zoom) are normal or "HD" which AFAICT is just changing whether it goes full resolution (1080p) or crops in to 720p. Maybe you're chewing up a lot of the pipeline? Since you do have your monitors on a dock. Resolution/Framerate? Lower it maybe? Just because it can doesn't mean it's good at it?
The dual external displays are on Displayport and HDMI, both connected to the TB3 dock (so they're driven via the internal video via Thunderbolt display transport, it's not a junky DisplayLink USB situation). It does have both Intel 630 graphics and a geforce GTX1650 in it, but I have no control over what is being used when, AFAIK.
The only video-related thing that has been "modified" is that I've used the Windows Store (which should be safe / benign, no?) to install HEIC/HEIV decoders. It's a bog standard W10 install as it came from Dell, I haven't installed any "codec packs" or any garbage like that on it. something, and it "hot bags" itself to death.) (I would just put it to sleep every night instead, but this particular model of Dell XPS has a habit of not actually going to sleep when you suspend it, or it wakes up whenever the hell it feels like it to do. So it can go a week or two between real reboots, even though it does get "powered off" each night. Normally I hibernate it at the end of the day, and then bring it back out when I come to work the next day (I take the laptop home at night just in case I need it outside normal hours). It seems like rebooting the laptop helps, at least for a while.
I'm leaning toward something software related, but I don't have the slightest clue where to start. Reboot helped improve it there, but again, same kind of behavior. The laptop's own internal camera does it too, from what I remember / the few times I've used it. Honestly, I wish they had given me a desktop instead of a laptop, but that's a complaint for another thread. Probably 90% of my usage is connected to the (Dell) thunderbolt 3 dock so I can use both monitors. I'm trying to avoid having the camera directly attached to the laptop as that makes things messy. I tried moving it directly to the laptop and it worked for a while, but IIRC it got weird there after a while too. I would just get a USB extension cable and run it right into the laptop. I'm betting on interference of some kind with the various devices. Try a call with it on the ports directly on the laptop. Odd, I just started a Zoom call and it's doing it again now, even though I've moved it off of the hub and over to the TB3 dock. So it must be something with the USB3 hub that's causing trouble for the webcam. Moved the webcam over to one of the ports on the TB3 dock, and it's still OK. I just tried moving the webcam directly into a USB3 port on the laptop, and the video problems went away. The webcam is plugged into an Anker USB3 hub, which is plugged into a Dell Thunderbolt3 Dock, which goes into a Dell XPS15 laptop. Sometimes it's partial flicker just at the bottom of the image, like i get a weird colored line.
I don't know how to describe this - the video sort of hiccups or "glitches," almost like it's blinking out and then coming back. Regardless of software (have tried Teams, Zoom, presume it happens with other stuff), I get the same behavior. Laptop is closed and connected to a dual-display setup via a Dell Thunderbolt 3 dock.
Windows 10 on a Dell XPS 15 laptop, current build, everything updated.