@davidgerard I've got an ezcap brand one that has worked pretty well: no special software needed as it presents as a standard USB video class device, and it has HDMI passthrough. It has even worked on USB 2.0 mode, offering MJPEG modes rather than raw YUV2. The only thing I don't like is the non-standard USB-A to USB-A cable it uses.

The model I've got is a bit old, but this seems to be the equivalent current model: https://www.ezcap.com/ezcap321. It seems the best way to get one is to pick one of the sellers on AliExpress at random.

I've also used some of the cheap dongles, which tend to work but have a lower quality output (e.g. they might only do MJPEG). That might be for recording from a camera, where that compression gives acceptable results.