Zoom Cannot Start Video With Older Webcams in Windows 10

I've had a Logitech QuickCam Fusion webcam since around the time Windows 7 was still mainstream. Other than from my work laptop I don't do online meetings so the camera largely went unused on my home desktop, even after upgrading to Windows 10. 

Then, one day my wife and I installed Zoom and wanted to test it out prior to her joining some Zoom calls with some of her old high school classmates. While her setup with Windows 10 and a relatively new (ca. 2021) webcam worked flawlessly, mine did not. Repeatedly Zoom would complain whether in the video settings or upon joining a meeting, "Cannot start video":

My solution took some trial and error but ultimately worked. First, unplug your webcam from its USB port, and then open Device Manager, and under Imaging devices, right-click on Logitech QuickCam Fusion (or whatever your older webcam is):

Ensure "Delete the driver software for this device" is checked so that whatever driver Windows may have initially used is removed, then click Uninstall and follow any prompts to remove the drivers:

Next, download and install the latest available drivers you can find for your old webcam, ideally for Windows 10, but at least for Windows 7. With some older webcams it's entirely possible you won't find any drivers let alone ones for Windows 7 or newer. If that's the case, skip the following.

Otherwise, on Logitech's site, upon searching for QuickCam Fusion, you'll notice the default operating system is set to Windows 11. Click and choose the only other option, Windows 7, and you'll be prompted to download the newest Windows drivers. 

Plug the webcam into a free USB port, and Windows will proceed to install either the driver you found and installed, or a compatible driver included with Windows. Assuming all goes well, from the Start menu type "Camera privacy settings" and ensure "Allow apps to access your camera" is set to On:

Further down the screen, ensure all apps (except Zoom, if listed) are set to Off:

Now, ensure "Allow desktop apps to access your camera" is set to On:

If you haven't already, install the latest Zoom desktop client. Before you proceed, go ahead and restart your PC to let Windows complete any post-configuration or housekeeping stuff that may linger. Then, once back at the desktop, create a system restore point to preserve things in case something blows up (unlikely, but always a possibility; my system decided to BSOD at least once during the process, better safe than sorry).

That's it. Upon opening Zoom and going into Settings => Video, you should see your face or whatever your webcam is currently seeing, and in meetings with video enabled things should proceed just fine.